**Potential and Kinetic Energy Study Questions** Class-8th Goyal Brothers ICSE Physics Solution Chapter-4 Unit-2 (Potential Energy and Kinetic Energy). We Provide Step by Step Answers of Study Questions Answer Type of Chapter-4 (Energy), unit-2 (Potential Energy and Kinetic Energy) Visit official Website **CISCE ** for detail information about ICSE Board Class-8.

## Potential and Kinetic Energy Study Questions Class-8th Goyal Brothers ICSE Physics Solution Chapter-4 Unit-2

Board | ICSE |

Class | 8th |

Subject | Physics |

Book Name | Goyal Brothers |

Chapter-4 | Energy |

Unit-2 | Potential Energy and Kinetic Energy |

Topic | Solution of exercise questions |

Session | 2023-24 |

**STUDY QUESTION**

Potential Energy and Kinetic Energy ICSE Class-8th Goyal Brothers Physics Solution Chapter-4 Unit-2

**Question: 1. (a) What do you understand by the term potential energy?**

**Answer: **The energy which a body possesses due to its position or due to a change in shape is called potential energy.

**(b) State two factors which determine potential energy of a body.**

**Answer: **Potential energy is determined by the following three factors:

- Mass of the body, m.
- Acceleration due to gravity, g.
- Height of the body, h.

**(c) Give four example of potential energy.**

**Answer: **Examples of Potential Energy:

1. A rock sitting at the edge of a cliff has potential energy. If the rock falls, the potential energy will be converted to kinetic energy.

2. Tree branches high up in a tree have potential energy because they can fall to the ground.

3. A stick of dynamite has chemical potential energy that would be released when the activation energy from the fuse comes into contact with the chemicals.

4. The food we eat has chemical potential energy because as our body digests it, it provides us with energy for basic metabolism.

**Question: 2. (a) What do you understand by the term kinetic energy?**

**Answer: **Kinetic energy is a form of energy that an object or a particle has by reason of its motion.

**(b) State two factors which determine kinetic energy of a body.**

**Answer: **Kinetic energy is determined by the following two factors:

- Mass of the body, m.
- Velocity of the body, v.

**(c) Give four examples of kinetic energy.**

**Answer: **Examples of Kinetic Energy:

1. An airplane has a large amount of kinetic energy in flight due to its large mass and fast velocity.

2. A baseball thrown by a pitcher, although having a small mass, can have a large amount of kinetic energy due to its fast velocity.

3. A downhill skier traveling down a hill has a large amount of kinetic energy because of their mass and high velocity.

4. A golf ball sitting on a tee before it is struck has zero kinetic energy because its velocity is zero.

**(d) Two bodies have equal mass. However, the speed of the one body is twice the speed of other body. What is the ratio of kinetic energy of the two bodies?**

**Answer: **The ratio of Kinetic energy of two bodies will be 1 : 4. Explanation: Kinetic energy is the energy posses by a body due to its state of motion. It is defined as the work needed to be done to accelerate a body of given mass ‘m’ from the rest to a certain velocity ‘v’.

**Question: 3. By giving an example, state and explain the law of conservation of energy.**

**Answer: **Energy can neither be related nor be destroyed Although, it may be transformed from one form to another form.

**Question: 4. A stone of weight 2kgf is lying on the roof of a building 60 m high. Calculate the amount of stored energy in the stone. [Take 1kgf = 10 N]**

**Answer: **Given: Weight = 2kgf

Height = h = 60m

1kgf = 10N ⇒ 2kgf = 2oN =mg = f

Stored energy = mgh = 20 × 60

= 1200J

**Question: 5. A stone of weight 0.25kgf is projected vertically upward such that it attains a height of 40 m. Calculate the amount of energy in the stone at the highest point. [Take 1kgf = 10 N]**

**Answer: **Given: Weight = 0.25kgf

Height = h = 40m

1kgf = 10N ⇒ 2kgf = 2oN =mg = f

Stored energy = mgh = 20 × 40

= 100J

**Question: 6. A boy of mass 50 kg climbs stairs by spending 1200 J of energy. How high does the boy climb up? [Take g = 10 ms¯²]**

**Answer: **Mass of boy (m) = 50kg

Acceleration due to gravity (g) = 10 ms¯²

The height achieved (h) = ?

Energy spent by boy (PE) = 1200J

Knowing, P.E. = mgh

1200J = 50 kg × 10 ms¯² × h

h = 1200/50 × 10

= 2.4 m.

**Question: 7. A stone of mass 0.10 kg is projected vertically upward by expending 80 J of energy. How high the stone rises? [Take g = 10 ms¯²]**

**Answer: **Given data = mass = 0.10 kg , Energy = 80J

g = 10 m/s²

Energy stored = m × g × h

80 = 0.10 × 10 × h

h = 80 m.

**Question: 8. State the kind of energy (potential or kinetic or both) in case of the following :**

**(a) Stone resting on the top of a hill.**

**Answer: **Potential Energy

**(b) An arrow shooting from a stretched bow and arrow system**

**Answer: **Both the energies

**(c) A flying mosquito**

**Answer: **Kinetic Energy

**(d) A wound-up spring of a toy car**

**Answer: **Potential Energy

**(e) A speeding car**

**Answer: **Kinetic Energy

**(f) A bullet fired from a gun**

**Answer: **Kinetic Energy

**Question: 9. 40 kg of water flows out of a tap at uniform speed of 5 ms¯¹. Calculate the amount of energy possessed by the water.**

**Answer:** Given: Mass, m = 40kg

Speed, v = 5 ms¯¹

Energy = ?

Water posses kinetic energy due to its flow.

Energy possessed = 1/2 × m × v²

= 1/2 × 40 × 5 × 5

= 500J

**Question: 10. A train of mass 100 tones is moving with a uniform speed of 2 ms¯¹. Calculate the amount of energy possessed by the train. [Take 1 tone = 1000 kg]**

**Answer: Energy of a moving body → Kinetic energy (KE)**

Kinetic energy = 1/2 mv²

m = 100ton = 100 × 1000kg = 100000kg

v = 2ms¯¹

Kinetic energy = 1/2 × 100000 × 2²

= 100000/2 × 4

**K.E. = 200,000J**

**Question: 11. A car expends an energy of 25,000 J while moving at a constant speed of 5 ms¯¹. What is the mass of car?**

**Answer: **Kinetic energy = 1/2 mv²

m = mass of the car

v = speed of the car

Kinetic energy = 25000J

v = 5 ms¯¹

Kinetic energy = 1/2 mv²

25000 = 1/2 m × 5²

25000 = 1/2 m × 25

1000 = 1/2m

**m = 2000kg**

**Question: 12. A vehicle expends an energy of 40000 J while moving at a constant speed of 10 ms¯¹. What is the mass of vehicle?**

**Answer: **Kinetic Energy = 4 × 10³J , v = 10m/s

Kinetic Energy = 1/2mv²

(4 × 10³J) = 1/2 × m × (10m/s)²

⇒ 2 × 4 × 10³/10² = m

2 × 4 × 10 = m

**m = 80 kg**

**— : end of Potential and Kinetic Energy Study Questions Class-8th Goyal Brothers ICSE Physics Solution Chapter-4 Unit-2:–-**

**Return to- ICSE Class -8 Goyal Brothers Physics Solutions**

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