Science: Conservation of Energy Worksheet

Question 1

State the law of conservation of energy in your own words.

Accepted Answer

The law of conservation of energy states that energy cannot be created or destroyed. It can only be transferred from one object to another or transformed from one form into another.

Question 2

A roller coaster starts at the top of a hill with a large amount of gravitational potential energy. As it moves down the hill, what happens to its potential energy and kinetic energy?

Accepted Answer

As the roller coaster moves down the hill, its gravitational potential energy decreases and its kinetic energy increases. The energy is transformed from potential energy into kinetic energy.

Question 3

A 2 kg book is held 5 m above the ground. Using g = 9.8 m/s^2, calculate its gravitational potential energy.

Accepted Answer

The gravitational potential energy is 98 joules because PE = mgh = 2 x 9.8 x 5 = 98 J.

Question 4

A moving cart has 120 J of kinetic energy. If friction does 30 J of work on the cart, how much kinetic energy remains if no other energy transfers occur?

Accepted Answer

The cart has 90 J of kinetic energy remaining. Friction removes 30 J from the cart's kinetic energy, so 120 J - 30 J = 90 J.

Question 5

Explain why a swinging pendulum never returns to exactly the same height if air resistance and friction are present.

Accepted Answer

A swinging pendulum does not return to exactly the same height because some of its mechanical energy is transformed into thermal energy and sound due to air resistance and friction. The total energy is still conserved, but less remains as mechanical energy.

Question 6

A 0.5 kg ball is dropped from a height of 10 m. Ignore air resistance. What is its speed just before it hits the ground? Use g = 9.8 m/s^2.

Accepted Answer

The speed just before impact is about 14 m/s. Using conservation of energy, mgh = 1/2 mv^2, so 0.5 x 9.8 x 10 = 1/2 x v^2, which gives v^2 = 196 and v = 14 m/s.

Question 7

A battery powers a flashlight. Describe the main energy transformations that take place.

Accepted Answer

In a flashlight, chemical energy stored in the battery is transformed into electrical energy. The electrical energy is then transformed mostly into light energy and some thermal energy.

Question 8

A spring stores 45 J of elastic potential energy. If all of this energy is converted into kinetic energy of a toy car, how much kinetic energy does the car have?

Accepted Answer

The toy car has 45 J of kinetic energy if all of the elastic potential energy is converted into kinetic energy. The total energy stays the same during the transformation.

Question 9

A student says, "Energy disappeared because the ball stopped moving." Explain why this statement is incorrect.

Accepted Answer

This statement is incorrect because the energy did not disappear. When the ball stopped moving, its kinetic energy was transformed into other forms such as thermal energy, sound, and energy transferred to the floor and surroundings.

Question 10

A 3 kg object moves at 4 m/s. Calculate its kinetic energy.

Accepted Answer

The kinetic energy is 24 joules because KE = 1/2 mv^2 = 1/2 x 3 x 4^2 = 1.5 x 16 = 24 J.

Question 11

In a hydroelectric dam, water stored behind the dam eventually helps produce electricity. Describe the sequence of major energy transformations.

Accepted Answer

In a hydroelectric dam, gravitational potential energy of the stored water is transformed into kinetic energy as the water falls. That kinetic energy turns turbines, creating mechanical energy, which is then transformed into electrical energy by a generator.

Question 12

A skater has 600 J of total mechanical energy at the top of a ramp. If the skater has 150 J of potential energy at one point on the ramp, how much kinetic energy does the skater have there, assuming no friction?

Accepted Answer

The skater has 450 J of kinetic energy at that point. Since total mechanical energy is 600 J and potential energy is 150 J, the kinetic energy must be 600 J - 150 J = 450 J.

Question 13

Why is food often described as stored chemical energy for the human body?

Accepted Answer

Food is described as stored chemical energy because its molecules contain energy in their chemical bonds. The body releases and transforms this energy during metabolism to support movement, growth, and maintaining body functions.

Question 14

A car engine converts gasoline's chemical energy into motion, but the process is not perfectly efficient. Where does much of the remaining energy go?

Accepted Answer

Much of the remaining energy is transformed into thermal energy that heats the engine and surrounding air. Some energy is also transferred as sound and through friction in moving parts.

Question 15

Give one real-world example of conservation of energy and explain the energy transformations involved.

Accepted Answer

One example is a toaster. Electrical energy is transformed mainly into thermal energy that heats the metal wires and the bread, with a small amount also transformed into light energy from the glowing wires.

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Science: Conservation of Energy

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