7.2 Kinetic Energy and the Work-Energy Theorem

Net work as energy transferred into motion, the one-half m v squared expression, and getting final speeds without any kinematics equation.

College Physics 2e, 7.2 Kinetic Energy and the Work-Energy Theorem

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10 exercises

7.2 Exercise 2

A roller coaster is set up with a track in the form of a perfect cosine. Describe and graph what happens to the kinetic energy of a cart as it goes through the first full period of the track.

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7.2 Exercise 4

In what direction relative to the direction of travel can a force act on a car (traveling on level ground), and not change the kinetic energy? Can you give examples of such forces?

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7.2 Exercise 6

You are participating in the Iditarod, and your sled dogs are pulling you across a frozen lake with a force of 1200 N while a 300 N wind is blowing at you at 135 degrees from your direction of travel. What is the net force, and will your kinetic energy increase or decrease?

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7.2 Exercise 8

You are launching a 0.315-kg potato out of a potato cannon. The cannon is 1.5 m long and is aimed 30.0 degrees above the horizontal. It exerts an average 45 N force on the potato. Ignoring friction, what is the kinetic energy of the potato as it leaves the muzzle of the potato cannon?

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7.2 Exercise 10

Describe a system in which the main forces acting are parallel or antiparallel to the center of mass, and justify your answer.

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7.2 Exercise 12

A child has two red wagons, with the rear one tied to the front by a (non-stretching) rope. If the child pushes on the rear wagon, what happens to the kinetic energy of each of the wagons, and the two-wagon system?

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7.2 Exercise 17

Compare the kinetic energy of a 20,000-kg truck moving at 110 km/h with that of an 80.0-kg astronaut in orbit moving at 27,500 km/h.

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7.2 Exercise 19

Confirm the value given for the kinetic energy of an aircraft carrier in the reference. You will need to look up the definition of a nautical mile (1 knot = 1 nautical mile/h).

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7.2 Exercise 21

A car’s bumper is designed to withstand a 4.0-km/h (1.12-m/s) collision with an immovable object without damage to the body of the car. The bumper cushions the shock by absorbing the force over a distance. Calculate the magnitude of the average force on a bumper that collapses 0.200 m while bringing a 900-kg car to rest from an initial speed of 1.12 m/s.

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7.2 Exercise 23

Using energy considerations, calculate the average force a 60.0-kg sprinter exerts backward on the track to accelerate from 2.00 to 8.00 m/s in a distance of 25.0 m, if he encounters a headwind that exerts an average force of 30.0 N against him.

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