Physics - Test 2

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 a car.
A slowly moving ship can have a greater momentum than a fast-moving racing car when ______.
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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 ______.
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 charge 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 on 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 _______.
Momentum is conserved in elastic and inelastic collisions.
In which is momentum conserved: an elastic collision or an inelastic collision?
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.
Railroad car A rolls at a certain speed and makes an inelastic collision with car B of the same mass. If the equally massive cars 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 _______.
12 kg*m/s. Momentum = mv.
What is the momentum of an 8.8-kg bowling ball rolling at 1.4m/s?
15kg*m/s. Impulse=FT.
What impulse occurs when an average force of 5.0N is exerted on a car for 3.0s?
19 N*s.
What is the magnitude of the impulse on an 7.2-kg ball rolling at 2.6m/s when it bumps into a pillow and stops?
The wreckage after collision is motionless.
Two automobiles, each of mass 800kg, are moving at the same speed, 19m/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.
A 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. Divide momentum by mass. 12 divided by 4.
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 only be zero 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 step 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
Earth would spin a bit slower.
If all people, animals, trains, and trucks all over the world began to walk or run towards the East (opposite of the direction of Earth’s spin), then
2 m/s.
A 5000-kg freight car moving at 2m/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 horizontal direction cancels to zero -AND- in the vertical direction equals the momentum of the firecracker before bursting.
When a vertically falling firecracker bursts, the vector sum of momentum fragments
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 100J.
Which requires more work: lifting a 5-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 %. Efficiency equation is is usable energy divided by total.
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?
880 J
Calculate the work done in lifting a 400-N barbell 2.2m above the floor.
880 J
What is the gain of potential energy of the barbell when it is lifted to this height?
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
100 J.
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
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
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
energy, speed, velocity, and momentum.
A moving object has
momentum
If the speed of a motor scooter doubles, which of the following also doubles?
nothing
When you and your snowboard are in motion, which of the following can be zero?
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
m/s
What are the units of measurement for tangential speed?
RPM
What are the units of measurement for rotational speed?
Tangential speed increases with distance.
On a rotating turntable, how does tangential speed vary with distance from the center?
Rotational speed is constant.
On a rotating turntable, how does 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?
7.6 N m
Calculate the torque produced by a 42-N perpendicular force at the end of a 0.18-m-long wrench.
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.
If 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?
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
sphere
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 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
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