Practice 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 capacity to do work or cause change in a physical system, measured in joules (J).

The 'currency' that makes things happen. It's what you need to move, heat, or change anything.

Showing a random 20 of 50 problems.

Example 1

easy
Name the energy transformations when a ball is thrown upward and comes back down.

Example 2

medium
A 1200 kg car speeds up from 10 m/s to 20 m/s. How much energy was added (its KE change)?

Example 3

hard
A 2 kg2\,\text{kg} block slides 5 m5\,\text{m} down a 30∘30^\circ incline with friction force 4 N4\,\text{N} (g=9.8g = 9.8). Find its KE at the bottom from rest.

Example 4

easy
Which has units of joules: force, power, or energy?

Example 5

challenge
A 4 kg block slides 3 m down a 30 degree frictionless incline (g = 9.8). Using energy ideas, find its speed at the bottom if it started at rest.

Example 6

easy
Name the energy form stored in a stretched spring.

Example 7

medium
A spring with k=200 N/mk = 200\,\text{N/m} is compressed 0.2 m0.2\,\text{m}. Find the elastic PE stored.

Example 8

easy
What is the SI unit of energy?

Example 9

challenge
A roller coaster car (500 kg) at the top of a 20 m hill moving 5 m/s reaches a second hill. Ignoring friction (g = 9.8), what is the maximum height of a hill it can just crest with zero speed?

Example 10

medium
A 0.2 kg ball rolls off a table 1 m high at 3 m/s (g = 9.8). Find its total mechanical energy relative to the floor.

Example 11

medium
When a car brakes to a stop, where does its kinetic energy go?

Example 12

hard
A 1000 kg1000\,\text{kg} car drives uphill, gaining 50 m50\,\text{m} height while increasing speed from 10 m/s10\,\text{m/s} to 20 m/s20\,\text{m/s} (g=9.8g = 9.8). Find the total energy delivered by the engine (ignore friction).

Example 13

easy
State the law of conservation of energy.

Example 14

medium
An athlete lifts a 40 kg40\,\text{kg} barbell 1.5 m1.5\,\text{m} in 1.5 s1.5\,\text{s} (g=9.8g = 9.8). Find the average power.

Example 15

medium
A 3 kg3\,\text{kg} block on a frictionless ramp drops 2 m2\,\text{m} vertically (g=9.8g = 9.8). Find its KE at the bottom from rest.

Example 16

medium
A 1000 kg1000 \text{ kg} car traveling at 20 m/s20 \text{ m/s} brakes to a stop. How much energy is dissipated as heat?

Example 17

easy
What is the SI unit of energy, and what equivalent units appear in other formulas?

Example 18

medium
A 2 kg object slides down a frictionless ramp from 5 m height (g = 9.8). What fraction of its initial PE is kinetic at a height of 2 m?

Example 19

hard
A 0.05 kg0.05\,\text{kg} ball is thrown up at 20 m/s20\,\text{m/s}. At its peak (g=9.8g = 9.8), find the maximum height (energy method).

Example 20

medium
A 0.5 kg0.5\,\text{kg} ball is dropped from 4 m4\,\text{m} (g=9.8 m/s2g = 9.8\,\text{m/s}^2). Ignore drag. Find its speed just before hitting the ground.
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