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physics Physics For High Schools (KS4)

Solved problems for the chapter:

Other Forms of Energy

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Detailed solution steps are available at:

https://en.openprof.com/wb/chapter:other_forms_of_energy/5103/

Example 1.

Describe the energy conversions for the given examples:

A tile falls from a roof.
A ball rolled down a slope.
A jumper jumps off a bridge while he is tied to an elastic rope (Bungee jumping).
An archer fires an arrow vertically upwards.
A weight attached to a rope is displaced slightly so that it swings on the rope.
A brake is applied on a car until it stops.

Example 2.

At the point of release, a ball has a potential energy of 20 J. What is its kinetic energy just before it touches the ground? If it bounces off the ground several times before coming to rest, by how much does its internal energy increases?

A ball of mass 0.4 kg falls from a height of 1.4 m. After the first bounce off the ground, it reaches a height of 0.8 m. By how much has its internal energy increased?

A ball rolls down a 6 m long and 2 m high slope. It has a potential energy of 12 J at the top of the slope.

Describe the energy conversions during rolling.
What is its kinetic energy at the foot of the slope?

(Apply the law of conservation of energy).

A 100 g arrow is shot vertically upwards with a bow and reaches a height of 40 m. What was the elastic energy of the bow at launch?

The tables below give energy values for different bodies. Calculate the missing energy in the tables:

First body:

Kinetic energy: Potential energy: Elastic energy: Total energy:
100 40 20 ?
Second body:

Kinetic energy: Potential energy: Elastic energy: Total energy:
0 ? 400 600
Third body:

Kinetic energy: Potential energy: Elastic energy: Total energy:
60 120 ? 240
Fourth body:

Kinetic energy: Potential energy: Elastic energy: Total energy:
? 60 40 160

A wagon with a mass of 6 tonnes crashes into a spring at a speed of . The spring is compressed by 40 cm when the wagon stops. What is the elastic energy of the spring?

A weight of 1 kg falls from a height of 40 m. Calculate the kinetic energy, potential energy, and total energy of the weight for every 10 m of fall.

(Acceleration due to gravity, )

A body has a total energy of 360 J. At the moment observed, its potential energy is three times the elastic energy and its kinetic energy is twice the elastic energy. Calculate all three energies.

10.

A stone weighing 50 g is shot vertically upwards with a catapult. When the catapult is taut, it has an elastic energy of 18 J. At what height after launch is the kinetic energy of the stone twice the potential?

11.

Which of the following statements are correct:

As a body falls, its kinetic and potential energies remain unchanged.
A plasticine falls to the ground and stops without bouncing. The potential energy before the fall is equal to the internal energy when it stops on the ground.
A parachutist falls evenly towards the ground. The potential energy of the parachute is converted into the internal energy of the parachute and the surrounding air during the fall.
An athlete throws a spear with the force of his body. After 50 m of flight, the spear sinks into the ground. The law of conservation of energy applies from the moment the athlete picks up the spear.
A pendulum oscillates from one extreme position to another. The total energy of the pendulum is equal to its kinetic energy at its lowest, i.e., equilibrium position.
A car accelerating up a hill applies the law of conservation of energy.

12.

A plasticine ball weighing 0.1 kg is thrown against the wall at a speed of . The plasticine clings to the walls and soothes. What does the kinetic energy turn into? Calculate the change in internal energy of plasticine.

13.

A gymnast weighing 60 kg jumps on a trampoline and pushes him 3 m high. What is the elastic energy of the trampoline at the start?

14.

A cyclist travels down a hill from rest at point X without pedalling. The cyclist applies his brakes and the cycle stops at point Y.

Which energy transfers have taken place between X and Y?

15.

The diagram shows part of a rollercoaster ride with the car at different positions. The car runs freely down from position X to position Y and up the hill on the other side.

What happens to the energy in the kinetic store and the gravitational potential store of the car as it moves from position X to position Y?

	energy in kinetic store	energy in gravitational potential store
A	decreases	decreases
B	decreases	increases
C	increases	decreases
D	increases	increases

16.

Which row about the change of energy in the energy store must be correct?

	process	energy store	change of energy in store
A	water pumped up to a high-altitude dam	gravitational potential energy of water	increases
B	water pumped up to a high-altitude dam	kinetic energy of water	decreases
C	air passes through a wind turbine	gravitational potential energy of air	increases
D	air passes through a wind turbine	kinetic energy of air	increases

17.

Brakes are used to slow down a moving car. Into which form of energy is most of the kinetic energy converted as the car slows down?

chemical
elastic
thermal
sound

18.

A tennis ball is dropped from position 1. It falls vertically onto a hard surface at position 2.

Which energy changes have taken place between position 1 and position 2?

19.

In which form is energy stored by stretching a spring?

chemical energy
elastic potential energy
gravitational potential energy
thermal energy

20.

A child pushes a toy car along a horizontal surface and then releases it. As the car slows down, what is the main energy transfer?

from chemical to thermal
from chemical to kinetic
from kinetic to gravitational (potential)
from kinetic to thermal

21.

A mass bounces up and down on a steel spring. The diagram shows the mass and the spring at different points during the motion.

At which point does the mass have the least gravitational potential energy and at which point is the most elastic energy stored in the spring?

	least amount of gravitational potential energy	most elastic energy stored in spring
A	mass moving down	mass moving up
B	mass moving down	lowest point
C	lowest point	mass moving up
D	lowest point	lowest point

22.

A stone falls. Which row gives the energy changes?

	gravitational potential energy	kinetic energy
A	decreases	decreases
B	decreases	increases
C	increases	decreases
D	increases	increases

23.

A man, attached to an elastic cord, jumps from a platform. He falls before starting to rise. The length of the unextended cord is . The diagrams show four successive stages in his fall. In which position is elastic (strain) energy and kinetic energy present?

24.

An object is falling through a vacuum. Which energy transfer is taking place?

gravitational potential to kinetic
gravitational potential to thermal
kinetic to gravitational potential
kinetic to thermal

Kinetic energy:	Potential energy:	Elastic energy:	Total energy:
100	40	20	?