13.1.A.1Multiple Choice
Which expression gives the translational kinetic energy of an object of mass m moving with speed v?
Select A, B, C, or D to check your answer.
Directions:Work each problem on your own paper first. For multiple choice, select A, B, C, or D. You will see right away whether you are correct. If you miss, you will see the most likely reason, and you can try again. For short response, type your answer, then compare it with the model solution. Questions mix the three essential knowledge statements of Topic 3.1 — the equation K = ½mv² and how K depends on v², kinetic energy as a scalar, and how kinetic energy depends on the observer's frame of reference. Round decimals to the nearest hundredth unless noted otherwise.
Which expression gives the translational kinetic energy of an object of mass m moving with speed v?
Select A, B, C, or D to check your answer.
A tennis ball of mass 0.057 kg leaves a serve at 50 m/s. (a) Find its kinetic energy. (b) After bouncing, the ball is moving at 25 m/s. Find its kinetic energy. (c) By what factor did the kinetic energy change when the speed was cut in half?
The speed of a cart triples while its mass stays the same. By what factor does the cart's translational kinetic energy change?
Select A, B, C, or D to check your answer.
A 4 kg block slides along a track. At one moment it moves at +3 m/s. After it bounces off a wall it moves at −3 m/s. (a) Find the block's kinetic energy before the bounce. (b) Find its kinetic energy after the bounce. (c) How do the two values compare, and what is the change in kinetic energy, ΔK?
A 4 kg cart has a translational kinetic energy of 50 J. What is the cart's speed?
Select A, B, C, or D to check your answer.
A 1500 kg car has 300,000 J of translational kinetic energy. (a) How fast is it moving? (b) The driver brakes until the car's speed is half its original value. What is its kinetic energy now? (c) How much kinetic energy was removed by the brakes?
A 2 kg ball moves in the −x direction at 3 m/s. What is the ball's translational kinetic energy?
Select A, B, C, or D to check your answer.
The graph shows the kinetic energy of a cart as a function of its speed. One point is marked: (3 m/s, 18 J). (a) Find the mass of the cart. (b) Find its kinetic energy at v = 6 m/s. (c) At what speed is its kinetic energy 50 J?
A passenger sits motionless in a seat on a train that is moving at 30 m/s relative to the ground. Which statement about the passenger's translational kinetic energy is correct?
Select A, B, C, or D to check your answer.
Two identical 3 kg carts move on a floor. Cart 1 moves east at 4 m/s. Cart 2 moves north at 4 m/s. (a) Find the kinetic energy of each cart. (b) Find the total kinetic energy of the two carts. (c) Would the total change if both carts moved east instead?
A 2 kg puck has velocity components vx = 6 m/s and vy = 8 m/s. What is the puck's translational kinetic energy?
Select A, B, C, or D to check your answer.
A 0.4 kg ball is thrown straight up at 12 m/s. (a) Find its kinetic energy at launch. (b) Find its kinetic energy at the highest point, where it is momentarily at rest. (c) Find the change in kinetic energy, ΔK, from launch to the highest point.
In an experiment, students measure the kinetic energy K of a cart of mass m at several speeds and then graph K (vertical axis) versus v² (horizontal axis). The graph is a straight line through the origin. What does its slope represent?
Select A, B, C, or D to check your answer.
A 5 kg cart rolls along a track and slows from 8 m/s to 2 m/s. (a) Find its initial kinetic energy. (b) Find its final kinetic energy. (c) Find the change in kinetic energy.
Which statement correctly describes translational kinetic energy as a scalar quantity?
Select A, B, C, or D to check your answer.
A 70 kg passenger sits still in a seat on a train moving at 30 m/s relative to the ground. Find the passenger's translational kinetic energy as measured by (a) an observer standing on the ground, (b) an observer on the train, and (c) an observer on a second train moving at 30 m/s in the opposite direction on a parallel track.
A 2 kg ball moves at 6 m/s relative to the ground. An observer who is moving at 4 m/s in the same direction as the ball measures the ball's translational kinetic energy. What value does she find?
Select A, B, C, or D to check your answer.
A 60 kg person walks at 2 m/s relative to a flatcar. The flatcar moves at 12 m/s relative to the ground. Find the person's kinetic energy (a) relative to the flatcar, (b) relative to the ground when she walks toward the front of the flatcar, and (c) relative to the ground when she walks toward the back.
A 1000 kg car travels at 20 m/s relative to the ground. A passenger in a truck moving at 10 m/s in the same direction as the car measures the car's kinetic energy. What does the passenger find?
Select A, B, C, or D to check your answer.
A 2 kg cart speeds up from 4 m/s to 6 m/s relative to the ground. (a) Find the change in the cart's kinetic energy as measured by an observer on the ground. (b) Find the change as measured by an observer who is moving at 4 m/s in the same direction as the cart. (c) Do the two observers agree on the value of ΔK? Do they agree that the cart gained kinetic energy?