The moving skateboard.
Which has a greater momentum: a heavy truck at rest or a moving skateboard?
its mass times velocity is greater than that of the car.
A slowly moving ship can have a greater momentum than a fast-moving racing car when _______.
Impulse is force times a time interval.
Distinguish between force and impulse.
increasing the force or increasing the time interval
An impulse can be increased by
product of force and time.
The quantity that is called impulse can be measured by the ______
F=ma=mΔv/Δt, so Ft=Δ(mv)
How is the impulse -momentum relationship related to Newton’s second law?
exert the greatest force over the longest time.
To impart the greatest momentum to an object, you must
Long contact time decreases the magnitude of the average force and is favorable.
When you are struck by a moving object, is it favorable that the object makes contact with you over a short time or over a long time?
The average force is increased.
Why is a force that is applied for a short time more effective in karate?
Yes, always.
Is it correct to say that, if no net impulse is exerted on a system, then no change in the momentum of the system will occur?
It means momentum does not change.
What does it mean to say that momentum is conserved?
whether the collision is elastic or inelastic
When two vehicles collide, momentum is conserved _______.
remains the same.
When a big fish swims into an oncoming smaller fish and swallows it, the momentum of the two-fish system _______.
The speed of car B is equal to the initial speed of A.
Railroad car A rolls at a certain speed and makes a perfectly elastic collision with car B of the same mass. After the collision, car A is observed to be at rest. How does the speed of car B compare with the initial speed of car A?
Their speed is half the initial speed of car A
If the equally massive cars of the preceding question stick together after colliding inelastically, how does their speed after the collision compare with the initial speed of car A?
vectorally add up to equal the initial momentum of the firecracker
When a falling firecracker explodes, the momenta of its pieces _______.
23 kg(m/s)
What is the momentum of an 7.8-kg bowling ball rolling at 3.0m/s ?
Impulse =ft
p=26kg(m/s)
p=26kg(m/s)
What impulse occurs when an average force of 9.0N is exerted on a cart for 2.9s ?
impulse = 22 N⋅s
What is the magnitude of the impulse on an 7.4-kg ball rolling at 3.0m/s when it bumps into a pillow and stops?
a. v = 3.6 ms
A 5.2-kg fish swimming 0.70m/s swallows an absentminded 1.0-kg fish swimming toward it at a speed that brings both fish to a halt immediately after lunch.art A
Find the speed of the approaching smaller fish before lunch.
Find the speed of the approaching smaller fish before lunch.
The wreckage after collision is motionless.
Two automobiles, each of mass 1400kg , are moving at the same speed, 17m/s , when they collide and stick together.In what direction and at what speed does the wreckage move if one car was driving north and one south.
momentum.
same-size iron ball and wooden ball are dropped simultaneously from a tower and reach the ground at the same time. The iron ball has a greater
3 m/s.
The speed of a 4-kg ball with a momentum of 12 kg m/s is
less momentum.
A large heavy truck and a small baby carriage roll down a hill. Neglecting friction, at the bottom of the hill, the baby carriage will likely have
flying in different directions.
The total momentum of a flock of identical birds could be zero only if the birds are
3,000 kg m/s.
A motorcycle of mass 100 kilograms slowly rolls off the edge of a cliff and falls for three seconds before reaching the bottom of a gully. Its momentum upon hitting the ground is
a corresponding change in momentum.
It is correct to say that impulse is equal to
lengthened time of contact.
Padded dashboards in cars are safer in an accident than non-padded ones because passengers hitting the dashboard encounter
stopping time is longer on the carpet
Compared with falling on a stone floor, a wine glass may not break when it falls on a carpeted floor because the
longer time.
If you can’t avoid being hit by a fast-moving object, you’ll suffer a smaller contact force if you can extend that force over a
greater with the brick wall.
Whether a truck comes to a stop by crashing into a haystack or a brick wall, the stopping force is
both the same
Whether a truck comes to a stop by crashing into a haystack or a brick wall, the impulse is
the target would be safer than the shooter.
A tiny gun made of a strong but very light material fires a bullet more massive than the gun itself. For such a weapon
cannon has much more mass than the cannonball.
A cannon recoils while firing a cannonball. The speed of the cannon’s recoil is relatively small because the
greater.
A heavy truck and a small car rolling down a hill at the same speed are forced to stop in the same amount of time. Compared with the force that stops the car, the force needed to stop the truck is
friction between his feet and the board.
Freddy Frog drops vertically from a tree onto a horizontally-moving skateboard. The reason he doesn’t slip off the skateboard is due to
both the same
You’re driving down the highway and a bug spatters into your windshield. Which undergoes the greater change in momentum during the time of contact?
move in the opposite direction at a lower speed.
An astronaut floating alone in outer space throws a baseball. If the ball moves away at 20 m/s, the astronaut will
2/3 m/s.
A 5000-kg freight car moving at 2 m/s collides with a 10,000-kg freight car at rest. They couple upon collision and move away at
6 m/s
A 5000-kg freight car collides with a 10,000-kg freight car at rest. They couple upon collision and move at 2 m/s. What was the initial speed of the 5000-kg car?
all the same
A red car has a head-on collision with an approaching blue car with the same magnitude of momentum. A green car driving with the same momentum as the other cars collides with an enormously massive wall. Which of the three cars will experience the greatest impulse?
at 45 degrees to the direction of either car before collision.
Two vehicles with equal magnitudes of momentum traveling at right angles to each other undergo an inelastic collision. The combined wreck moves in a direction
greater than the magnitude of momentum of either car before collision.
Two vehicles with equal magnitudes of momentum traveling at right angles to each other undergo an inelastic collision. The magnitude of momentum for the combined wreck is
continue along the path as if the explosion didn’t occur.
A cannonball following a parabolic path explodes into fragments. The momentum of the fragments
in the vertical direction equals the momentum of the firecracker before bursting.
in the horizontal direction cancels to zero.
*both of these
neither of these
in the horizontal direction cancels to zero.
*both of these
neither of these
When a vertically falling firecracker bursts, the vector sum of momentum fragments
Momentum is conserved in elastic and inelastic collisions.
In which is momentum conserved: an elastic collision or an inelastic collision?
the momentum of the cannon is equal to the magnitude of the momentum of the cannon ball and points in the opposite direction.
When a cannonball is fired, the momentum of the system (cannon + cannonball) is conserved if
either of these depending on speed
Which has the greater momentum when moving?
reduced impulse.
reduced momentum.
both of these
*neither of these
reduced momentum.
both of these
*neither of these
When Peter tosses an egg against a sagging sheet, the egg doesn’t break due to
1.5 g.
A bungee jumper attains a speed of 30 m/s just as the bungee cord begins to stretch. If the period of stretch is 2 s while coming to a halt, the jumper’s average deceleration is about
exhaust gases.
The force that accelerates a rocket in outer space is exerted on the rocket by the
an impulse.
a decreasing acceleration.
an increasing speed.
*all of the above
a decreasing acceleration.
an increasing speed.
*all of the above
As Bronco Brown steps off a hovering high-flying helicopter and falls through the air, he experiences
zero
Two billiard balls having the same mass and speed roll toward each other. What is their combined momentum after they meet?
move away from each other, but at different speeds.
If a monkey floating in outer space throws his hat away, the hat and the monkey will both
decreases
An open freight car rolls friction free along a horizontal track in a pouring rain that falls vertically. As water accumulates in the car, the car’s speed
1 m/s.
A 2-kg rifle that is suspended by strings fires a 0.01-kg bullet at 200 m/s. The recoil velocity of the rifle is about
1/6 m/s.
A 5-kg shark swimming at 1 m/s swallows an absent-minded 1-kg fish swimming toward it at 4 m/s. The speed of the shark after his meal is
8 m/s.
3 m/s.
4 m/s.
6 m/s.
*none of the above
3 m/s.
4 m/s.
6 m/s.
*none of the above
A sandbag motionless in outer space is hit by a three-times-as massive sandbag moving at 12 m/s. They stick together and move at a speed of
joule
What is the unit of work?
work
A force sets an object in motion. When the force is multiplied by the time of its application, we call the quantity impulse, and an impulse changes the momentum of that object. What do we call the quantity force multiplied by distance?
zero
How much work is done on a satellite in a circular orbit about Earth?
Both take the same 1000 J.
Which requires more work: lifting a 50-kg sack a vertical distance of 2 m or lifting a 25-kg sack a vertical distance of 4 m?
Lifted in the same time, the power is the same. The light sack moving in half the time requires double the power.
If both sacks in the preceding question are lifted their respective distances in the same time, how does the power required for each compare? How about for the case in which the lighter sack is moved the same distance in half the time?
The car with twice the mass has twice the potential energy.
Two cars are raised to the same elevation on service-station lifts. If one car is twice as massive as the other, compare their gains of potential energy.
It would have twice as much potential energy.
A car is raised a certain distance in a service-station lift, thus giving it potential energy relative to the floor. If it were raised twice as high, how much more potential energy would it have?
It has four times as much.
When the speed of a moving car is doubled, how much more kinetic energy does it have?
four times.
When you lift twice the load twice as high, in half the time, the increase in potential energy is _______.
It takes four times the work and four times the stopping distance.
Compared with a car moving at some original speed, how much work must the brakes of a car supply to stop a car that is moving twice as fast? How will the stopping distances compare?
300 J
If you push a crate horizontally with 100 N across a 10-m factory floor and the friction between the crate and the floor is a steady 70 N, how much kinetic energy does the crate gain?
destroyed.
Energy cannot be _______.
10 kJ
What will the kinetic energy of a pile driver ram be if it starts from rest and undergoes a 10 kJ decrease in potential energy?
150 N
A force of 50 N is applied to the end of a lever, which is moved a certain distance. If the other end of the lever moves one-third as far, how much force does it exert?
50 %
When the useful energy output of a simple machine is 100 J, and the total energy input is 200 J, the efficiency is _______.
The Sun
What is the ultimate source of the energy from fossil fuels, dams, and windmills?
W = 650 J
Calculate the work done in lifting a 540-N barbell 1.2m above the floor.
ΔU = 650 J
What is the gain of potential energy of the barbell when it is lifted to this height?
F = 170 N
Nellie Newton applies a force of 56N to the end of a lever, which is moved a certain distance.If the other end of the lever moves one-third as far, find the force it exerts.
2 w
The power expended doing 100 J of work in 50 s is
6 w
The power required to exert 4-N force over 3 meters in 2 seconds is
the same.
Both a 50-kg sack is lifted 2 meters from the ground and a 25-kg sack is lifted 4 meters in the same time. The power expended in raising the 50-kg sack is
location.
An object has gravitational potential energy due to its
twice as much.
Relative to an initial height, an object raised twice as high has a gravitational potential energy
twice as much.
A crate of grapes lifted 10 meters gains 200 J of potential energy. If the same crate is instead lifted 20 meters, its gain in potential energy is
80 J.
A 2-kg ball is held 4 m above the ground. Relative to the ground its potential energy is
moving.
An object that has kinetic energy must be
four times the kinetic energy
Two identical golf carts move at different speeds. The faster cart has twice the speed and therefore has
100j
A melon is tossed straight upward with 100 J of kinetic energy. If air resistance is negligible the melon will return to its initial level with a kinetic energy of
less than 100 J.
A melon is projected into the air with 100 J of kinetic energy in the presence of air resistance. When it returns to its initial level its kinetic energy is
a car of half the mass traveling at 60 km/hr
Which has greater kinetic energy?
-both the same
-a car of half the mass traveling at 60 km/hr
-a car traveling at 30 km/hr
-need more information
100 J.
Neglecting air resistance, Sammy Smarts on a high ladder releases a ball that strikes the ground with 100 J of kinetic energy. If he were to instead throw the ball straight upward, it will soon reach the ground with a kinetic energy of
more than the golf ball.
If a Ping-Pong ball and a golf ball both move in the same direction with the same amount of kinetic energy, the speed of the Ping-Pong ball must be
75 j
Two identical particles move toward each other, one twice as fast as the other. Just before they collide, one has a kinetic energy of 25 J and the other 50 J. At this instant their total kinetic energy is
heat
When Joshua brakes his speeding bicycle to a stop, kinetic energy is transformed to
twice as far.
Two identical arrows, one with twice the kinetic energy of the other, are fired into a bale of hay. Compared with penetration of the slow arrow, the faster arrow penetrates
four times as far.
Two identical arrows, one with twice the speed of the other, are fired into a bale of hay. Compared with penetration of the slow arrow, the faster arrow penetrates
the top.
A ball rolling down an incline has its maximum potential energy at
the bottom.
A ball rolling down an incline has its maximum kinetic energy at
bottom of its swing.
The bob of a simple pendulum has its maximum kinetic energy at the
the same as its potential energy.
After rolling halfway down an incline, a marble’s kinetic energy is
halfway down.
A block of ice sliding down an incline has half its maximum kinetic energy
momentum.
kinetic energies.
potential energies.
inertias.
*none of the above
kinetic energies.
potential energies.
inertias.
*none of the above
A light aluminum ball and a heavy lead ball of the same size roll down an incline. When they are halfway down the incline, they will have identical
true
Strictly speaking, more fuel is consumed by your car if the air conditioner, headlights, or even a radio is turned on. This statement is
Art has half the mass of Bart.
Acrobat Bart at the circus drops vertically onto the end of a see-saw, with his partner Art equidistant from the fulcrum at the other end. Art is propelled straight upward a distance twice that of Bart’s dropping distance. Neglecting inefficiencies we see
more than 2.0 J.
A 1-kg ball dropped from 2 m rebounds only 1.5 m after hitting the ground. The amount of energy converted to heat is about
no perpetual-motion device that multiplies energy exists.
Although perpetual motion is the natural order of things in the universe
a fantasy.
A machine that promises more energy output than input is
energy conservation.
Newton’s Cradle consists of an aligned row of identical elastic balls suspended by strings so they barely touch one another. When two balls are raised from one end and released, they strike the row and two balls pop out from the other end. If instead, one ball popped out with twice the speed of the two, this would violate
distance that a force acts
Impulse involves the time that a force acts, whereas work involves the
all of these
A moving object has
momentum.
energy.
speed.
velocity.
all of these
momentun
If the speed of a motor scooter doubles, which of the following also doubles?
none of the above
When you and your snowboard are in motion, which of the following can be zero?
momentum
kinetic energy
mass
inertia
none of the above
energy
Two 2-m/s pool balls roll toward each other and collide. Suppose after bouncing apart each moves at 4 m/s. This collision violates the conservation of
four times as much.
The work you do when pushing a shopping cart twice as far while applying twice the force is
energy
The unit kilowatt-hour is a unit of
The energy is kinetic energy before it hits the ground; it is thermal energy after
An apple hanging from a limb has potential energy because of its height. If it falls, what becomes of this energy just before it hits the ground? When it hits the ground?
40 j
The work done in pushing a TV set a distance of 2 m with an average force of 20 N is
the force on the ball is at right angles to the ball’s motion.
No work is done by gravity on a bowling ball that rolls along a bowling alley because
3.6 million joules.
One kilowatt-hour represents
v = squareroot2gh
Emily holds a banana of mass m over the edge of a bridge of height h. She drops the banana and it falls to the river below.Use conservation of energy to find the speed of the banana just before hitting the water.
W = 750 J
How much work is done when you push a crate horizontally with 150N across a 5.0-m factory floor?
10%
A machine puts out 100 watts of power for every 1000 watts put into it. The efficiency of the machine is
400 j
If the force of friction on the crate is a steady 70 N, find the KE gained by the crate.
350 J
Find the energy turned into heat.
m/s for tangential, RPM for rotational
What are the units of measurement for tangential speed? For rotational speed?
Tangential speed increases with distance. Rotational speed is constant.
On a rotating turntable, how do tangential speed and rotational speed vary with distance from the center?
greater than toward the center
The tangential speed on the outer edge of a rotating carousel is _______.
Most of the mass is concentrated far from the axis.
How is a flywheel constructed to maximize its rotational inertia?
It increases.
As distance increases between most of the mass of an object and its center of rotation, how does rotational inertia change?
Axis along the lead, through the center, through one end
Consider three axes of rotation for a pencil: along the lead, at right angles to the lead at the middle, and at right angles to the lead at one end. Rate the rotational inertias about each axis from smallest to largest.
The solid disk will because the mass is closer to the axis of rotation.
Which will have the greater acceleration rolling down an incline: a hoop or a solid disk? Why?
Somewhere straight below where your hands grab the rope
If you hang at rest by your hands from a long vertical rope, where is your center of gravity with respect to the rope?
In the center of the ball
Where is the center of mass of a hollow soccer ball?
A vertical line through the center of gravity passes inside its support base.
Why doesn’t the Leaning Tower of Pisa topple over?
A vertical line through the center of gravity of your body is in front of the tips of your toes, which is outside your support base.
Why can’t you stand with your heels and back to a wall and then bend over to touch your toes and return to your stand-up position?
Toward the center of the circle
When you whirl a can at the end of a string in a circular path, what is the direction of the force you exert on the can?
quadruples the tension in the string
When a rock tied to a string is whirled in a horizontal circle, doubling the speed _______.
No force; Newton’s first law
If the string that holds a whirling can in its circular path breaks, what kind of force causes it to move in a straight- line path: centripetal, centrifugal, or no force? What law of physics supports your answer?
τ = 6.0 Nm
Calculate the torque produced by a 40-N perpendicular force at the end of a 0.15-m-long wrench.
Centripetal Force: F=mv2/r
F = 5.6 N
Calculate the tension in a horizontal string that whirls a 1.8-kg toy in a circle of radius 2.0m when it moves at 2.5m/s on an icy surface.
L = 170 kg⋅m2s
Calculate the angular momentum of the person if the force of friction that keeps a 80-kg person sitting on the edge of a horizontal rotating platform when the person sits 1.8m from the center of the platform and has a tangential speed of 1.2m/s .
one near outer rail
Which horse moves faster in m/s on a merry-go-round?
doubles
Your pet hamster sits on a record player that has constant angular speed. If the hamster moves to a point twice as far from the center, then its linear speed
directed toward the center of the curve.
The net force exerted on a car traveling in a circular path at constant speed is
62.8 m/min.
you’re on a Ferris wheel at a carnival, seated 10 m from the Ferris wheel’s axis that makes a complete rotation each minute, your linear speed is
straight.
The rotational inertia of your leg is greater when your leg is
bent
You can swing your legs to and fro more frequently when your legs are
mouse
Which of these animals has a quicker stride?
mouse
cat
giraffe
horse
mouse
cat
giraffe
horse
four times greater.
A flywheel’s diameter is twice that of another of the same shape and mass. Rotational inertia of the larger flywheel is
two times greater
Consider two flywheels of the same size and shape, but one with twice the mass. Rotational inertia of the more massive one is
coin
A coin and a ring roll down an incline at the same time. The one to first reach the bottom is the
spere
A ring, a disk, and a solid sphere begin rolling down a hill together. Which reaches the bottom first?
with water
Which tin can will roll down an incline in the shortest time, one filled with water or one filled with ice? (Hint: water ‘slides’ inside the can.)
above a place of support.
The famous Leaning Tower of Pisa doesn’t topple over because its center of gravity is
remains the same, but the revolutions per minute decrease.
As you crawl toward the edge of a large freely-rotating horizontal turntable in a carnival funhouse, the angular momentum of you and the turntable
through its center of gravity.
to kick a football so it won’t topple end over end, kick it so the force of impact extends
at the center of the Earth
If Earth had a pair of identical moons on opposite sides of the same circular orbit, the center of gravity of the double-moon-Earth system would be
1 kg
A 1-kg rock is suspended from the tip of a horizontal meterstick at the 0-cm mark so that the meterstick barely balances like a seesaw when its fulcrum is at the 25-cm mark. From this information, the mass of the meterstick is
none of the above
A 1-kg rock is suspended from the tip of a horizontal meterstick at the 0-cm mark so that the meterstick barely balances like a seesaw when its fulcrum is at the 12.5-cm mark. From this information, the mass of the meterstick is
the same
You can safely stand on the overhanging end of a heavy plank that rests on a table. How much overhang depends on your mass and the plank’s mass. If you can stand on the end of a plank that overhangs the edge of the supporting table 1/4 its total length, how massive is the plank compared to your mass?
1/3 the distance from the fulcrum.
On a balanced seesaw, a boy three times as heavy as his partner sits
rise.
Two people are balanced on a seesaw. If one person leans inward toward the center of the seesaw, that person’s end of the seesaw tends to
wide handle
To rotate a stubborn screw, it is best to use a screwdriver that has a
2/3
You can safely stand on the overhanging end of a heavy plank that rests on a table. How much overhang depends on your mass and the mass of the plank. If you can stand on the end of a plank that overhangs the edge of the supporting table 1/5 its total length, how massive is the plank compared to your mass?
increases
When a twirling ice skater brings her arms inward, her rotational speed
rotates faster.
As a huge rotating cloud of particles in space gravitate together forming an increasingly dense ball, it shrinks in size and
Angular momentum does not change without an applied external torque.
What is the law of inertia for rotating systems in terms of angular momentum?
Her angular momentum does not change. Her spin rate doubles.
If a skater who is spinning pulls her arms in so as to reduce her rotational inertia by half, by how much will her angular momentum change? By how much will her rate of spin change?
Torque tends to twist or change the state of rotation of the object.
Her angular momentum does not change. Her spin rate doubles.
about its end, like a pendulum.
Torque tends to twist or change the state of rotation of the object.
droops
A tightrope walker more easily balances on a tight wire if her pole
the filled one
Which jar will roll down an incline in the shortest time, an empty one or one filled with peanut butter?
all of above
Compared with a force, a torque involves
Compared with a force, a torque involves
distance from an axis of rotation.
rotation.
leverage.
all the above
Compared with a force, a torque involves
distance from an axis of rotation.
rotation.
leverage.
all the above
both
A ball that gains speed as it rolls down a hill experiences a
net torque.
net force.
both of these
neither of these
net torque.
net force.
both of these
neither of these
ROATATION
A torque acting on an object tends to produce
more than the weight of the seesaw.
A solitary boy cannot balance on a seesaw with its fulcrum at its midpoint. If the fulcrum is moved to one-quarter the distance from the boy, balance is achieved when the weight of the boy is
rotating
Centrifugal forces are an apparent reality to observers in a reference frame that is
the radial component of the normal force.
The force responsible for a car moving steadily along a no-friction icy banked curve is due to
Centripetal force does no work on a circularly-moving object because
Centripetal force does no work on a circularly-moving object because
longer
As the polar icecaps melt, the resulting water spreads over the entire Earth. This new mass distribution tends to make the length of a day
18nm
To tighten a bolt, you push with a force of 72N at the end of a wrench handle that is 0.25m from the axis of the bolt.
what torgue are you exerting?
what torgue are you exerting?
180N
If you move your hand inward to be only 0.10 m from the bolt, find the force that you should exert to achieve the same torque.
1.1 kg
Think And Solve 8.46
The rock and meterstick balance at the 25-cm mark, as shown. The meterstick has a mass of 1.1kg what the mass of rock
The rock and meterstick balance at the 25-cm mark, as shown. The meterstick has a mass of 1.1kg what the mass of rock
