Practice Kinetic Energy in Physics

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

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Quick Recap

The energy an object possesses by virtue of its motion, equal to one-half times its mass times the square of its velocity.

The faster something moves and the heavier it is, the more kinetic energy it has.

Showing a random 20 of 50 problems.

Example 1

hard
A 2 kg2\text{ kg} block slides on a horizontal surface with friction coefficient μk=0.3\mu_k = 0.3. It starts at 5 m/s5\text{ m/s}. How far does it travel before stopping (use g=9.8 m/s2g = 9.8\text{ m/s}^2)?

Example 2

medium
A 5 kg object loses 60 J of KE, slowing from some speed to 2 m/s. What was its initial speed?

Example 3

challenge
A 200 g200\text{ g} pendulum bob swings down from rest at a height hh above its lowest point. At the bottom its speed is 4 m/s4\text{ m/s}. Find hh (use g=9.8 m/s2g = 9.8\text{ m/s}^2).

Example 4

medium
A bullet (0.02 kg) and a runner (60 kg) both have KE = 100 J. Which moves faster, and what is the bullet's speed?

Example 5

medium
A 0.04 kg0.04\text{ kg} arrow leaves a bow with KE=50 JKE = 50\text{ J}. Find its launch speed.

Example 6

medium
A 1200 kg1200\text{ kg} car accelerates from 10 m/s10\text{ m/s} to 25 m/s25\text{ m/s}. How much work was done on it (assuming no losses)?

Example 7

easy
A 6 kg6\text{ kg} box slides at 2 m/s2\text{ m/s}. Find its kinetic energy.

Example 8

medium
A roller coaster car (500 kg500\text{ kg}) descends a 20 m20\text{ m} hill from rest. Ignoring friction and using g=9.8 m/s2g = 9.8\text{ m/s}^2, find its kinetic energy at the bottom.

Example 9

easy
A 1 kg ball at rest. What is its kinetic energy?

Example 10

challenge
A 1000 kg car at 30 m/s and a 2000 kg truck at 15 m/s. Which has more kinetic energy, and what is the ratio car:truck?

Example 11

easy
A 0.5 kg0.5\text{ kg} ball has kinetic energy 36 J36\text{ J}. Find its speed.

Example 12

easy
A 2 kg object moves at 3 m/s. Find its kinetic energy.

Example 13

medium
A 0.5 kg ball moving at 6 m/s is brought to rest. How much energy must be removed?

Example 14

easy
A 4 kg object moves at 5 m/s. What is its kinetic energy?

Example 15

easy
If speed doubles, by what factor does kinetic energy change?

Example 16

challenge
Total kinetic energy of a hoop (mass mm, radius RR) rolling without slipping at speed vv is KE=12mv2+12Iω2KE = \tfrac{1}{2}mv^2 + \tfrac{1}{2}I\omega^2 with I=mR2I = mR^2. Find the total kinetic energy as a multiple of 12mv2\tfrac{1}{2}mv^2.

Example 17

easy
A 10 kg object has KE = 80 J. What is its speed?

Example 18

challenge
A proton and an alpha particle (mass 4 times the proton) have equal kinetic energy. Find the ratio of their speeds (proton:alpha).

Example 19

easy
A 0.2 kg0.2\text{ kg} apple falls and just before hitting the ground has KE=4 JKE = 4\text{ J}. Find its speed at that instant.

Example 20

challenge
A 0.02 kg0.02\text{ kg} bullet at 300 m/s300\text{ m/s} embeds itself in a 2 kg2\text{ kg} block at rest on a frictionless surface. Find the kinetic energy lost to deformation and heat.
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