it is speeding up
If there is a net positive force on an object, then…
There is no net work.
A person applies a 50 N force on a crate, causing it to move horizontally at a constant speed through a distance of 10 m. What is the net work done on the crate?
Work done by gravity is negative while the ball is traveling upward and positive while the ball is traveling downward.
A ball is thrown straight upward. How does the sign of the work done by gravity while the ball is traveling upward compare with the sign of the work done by gravity while the ball is traveling downward?
The two objects rise to the same height.
Two objects are moving at equal speed along a level, frictionless surface. The second object has twice the mass of the first object. They both slide up the same frictionless incline plane. Which object rises to a greater height?
The maximum height of the second ball is four times that of the first ball.
Two identical balls are thrown vertically upward. The second ball is thrown with an initial speed that is twice that of the first ball. How does the maximum height of the two balls compare?
The speed of the freight car decreases.
A freight car moves along a frictionless level railroad track at constant speed. The freight car is open on the top. A large load of sand is suddenly dumped into the freight car. What happens to the speed of the freight car?
The total momentum of the system is conserved.
When a person steps forward out of a small boat onto a dock, the boat recoils backward in the water. Why does this occur?
The ball experiences the greater momentum change.
A lump of putty and a rubber ball have equal mass. Both are thrown with equal speed against a wall. The putty sticks to the wall. The ball bounces back at nearly the same speed with which it hit the wall. Which object experiences the greater momentum change?
The impulse is the same in both situations.
In a lab environment, you are investigating the impulse of a force exerted on a brick when the brick’s speed is reduced from 2.5 m/s to a complete stop. First, you allow the brick to slam into a secured piece of wood, bringing the brick to a sudden stop. Second, you allow the brick to plow into a large slab of gelatin so that the brick comes to a gradual halt. In which situation is there a greater impulse of the force on the brick?
momentum is conserved and kinetic energy is conserved.
For an elastic collision…
The velocity of the red ball is −2.0 m/s; the velocity of the yellow ball is +3.0 m/s.
A red ball with a velocity of +3.0 m/s collides head-on with a yellow ball of equal mass moving with a velocity of −2.0 m/s. What is the velocity of the two balls after the elastic collision?
The force applied at the doorknob exerts the greater torque.
Two equal forces are applied perpendicular to a door. The first force is applied at the midpoint of the door; the second force is applied at the doorknob. Which force exerts the greater torque?
The object will rotate with constant angular acceleration.
A constant net torque is applied to a rotating object. Which of the following best describes the object’s motion?
The side the boy is sitting on will tilt downward.
A heavy boy and a lightweight girl are balanced on a massless seesaw. The boy moves backward, increasing his distance from the pivot point. What happens to the seesaw?
A scalar is specified with a single number, but a vector is specified using both a magnitude and a direction.
In the study of physics, what distinguishes a scalar from a vector?
5, and 240 degrees
The magnitude is not negative, because the direction (angle) gives that value.
Vector A⃗ has a magnitude of 10 and a direction angle of 60º. What is the magnitude and direction angle (as measured counterclockwise from the positive x-axis) of −A⃗ /2?
7.00 m
Vector A⃗ has a magnitude of 2.00 m and vector B⃗ has a magnitude of 5.00 m. If the direction of each vector is unknown, what is the largest possible value for the magnitude of A⃗ −B⃗ ?
6.00 km
Starting from your campsite you walk 3.0 km east, 6.0 km north, 1.0 km east, and then 4.0 km west. How far are you from your campsite?
The horizontal component of a projectile’s acceleration is zero.
For general projectile motion, which of the following best describes the horizontal component of a projectile’s acceleration? Assume air resistance is negligible.
The vertical component of a projectile’s acceleration remains a nonzero constant.
For general projectile motion, which of the following best describes the vertical component of a projectile’s acceleration? Assume air resistance is negligible.
The speed at its highest point is less than its initial speed.
(horizontal stays same, vertical follows gravity)
(horizontal stays same, vertical follows gravity)
A player kicks a soccer ball in a high arc toward the opponent’s goal. When the soccer ball reaches its maximum height, how does its speed at this point compare to its initial speed? Assume air resistance is negligible.
At the maximum height, the velocity and acceleration vectors are perpendicular to each other.
A football player kicks a football in a field goal attempt. When the football reaches its maximum height, what is the relationship between the direction of the velocity and acceleration vectors? Assume air resistance is negligible.
The two balloons hit the ground at the same time.
A red water balloon is thrown horizontally from the top of a bridge. At the same instant, a yellow water balloon is dropped off the bridge from the same height. Compare the time of fall for the two balloons. Assume air resistance is negligible.
The plane will be located directly above the package.
A pilot releases a package from a plane flying horizontally at a constant speed. When the package reaches the ground below, what is the horizontal location of the plane with respect to the package? Assume air resistance is negligible.
The object will continue to move with a constant velocity.
An object is moving in the absence of a net force. Which of the following best describes the object’s motion?
The net force acting on the object is zero.
An object is moving with constant velocity. Which of the following best describes the force(s) acting on the object?
The acceleration of object 1 is twice the acceleration of object 2.
The same net force is applied to two different objects. The second object has twice the mass of the first object. Compare the acceleration of the two objects.
The force on the truck is equal to the force on the car.
A large truck collides head-on with a small car. The car is severely damaged as a result of the collision. According to Newton’s third law, how do the forces acting between the truck and car compare during the collision?
The coefficient of static friction is greater than the coefficient of kinetic friction.
In general, how does the coefficient of static friction compare to the coefficient of kinetic friction for the same two materials?
The velocity and acceleration vectors are perpendicular.
An object moves in a circular path at a constant speed. What is the relationship between the directions of the object’s velocity and acceleration vectors?
The net force is directed toward the center of the circular path.
An object moves in a circular path at a constant speed. What is the direction of the net force acting on the object?
The gravitational force increases by a factor of 4.
Two objects attract each other gravitationally. If the distance between their centers decreases by a factor of 2, how does the gravitational force between them change?
The gravitational force increases by a factor of 4.
Two objects attract each other gravitationally. If the mass of each object doubles, how does the gravitational force between them change?
The acceleration due to gravity is g/27.
A hypothetical planet has a mass one-third of and a radius three times that of Earth. What is the acceleration due to gravity on the planet in terms of g, the acceleration due to gravity on Earth?
Earth’s orbital speed is greater when it is closer to the Sun than when it is farther from the Sun.
Earth’s orbit around the Sun is slightly elliptical. Thus, Earth actually gets closer to the Sun during part of the year. What happens to Earth’s orbital speed when it is closer to the Sun?
