Law of Conservation of Energy

Q. What is the difference between kinetic and potential energy?

Q.

derive the formula of kinetic energy and potential energy

Q.

(a) State and explain the law of conservation of energy with an example.

(b) Explain how the total energy of a swinging pendulum at any instant of time is conserved. Illustrate your answer with the help of a labelled diagram.

Q.

What is the unit of potential energy?

Q.

A body of mass 10 kg is dropped from a height of 20 m. Find (i) its potential energy before it is dropped, (ii) its kinetic energy when it is 8 m above the ground and (iii) its kinetic energy when it hits the ground.
Take g = 10 ms.

Q. State the principle of conservation of energy.

Q. If a body of mass 3 kg is dropped from the top of a tower of height 250 m, then its kinetic energy after 3 s will be

1. $1126J$
2. $1048J$
3. $735J$
4. $1296.5J$

Q.

Explain the energy transformations in the Solar cell?

Q.

Why is electric energy the most desirable form of energy?

Q.

When a body falls freely towards the earth, then total energy

1. Increases

2. Decreases

3. Remains constant

4. First increases and then decreases

Q.

Which of the following statement is/are true for a freely falling body?

1. Potential energy and kinetic energy at any point during the free fall always remain constant.

2. Potential energy gets converted into kinetic energy progressively.

3. Sum of potential energy and kinetic energy at any point during the free fall remains constant.

4. Sum of potential energy and kinetic energy at any point during the free fall does not remain constant.

Q.

An object of mass $10kg$ falls from height $10m.$ Kinetic energy gained by the body will be approximately equal to:

1. $1000J$

2. $500J$

3. $100J$

4. None of these

Q. The energy of 4900 joule was expanded in lifting a 50 kilogram of mass what is the height?

Q.

A ball of mass 200 g falls from a height of 5 metres. What is the kinetic energy when it just reaches the ground? (g = 9.8 $m/s^2$).

Q.

Question 9
A body is falling from a height h, after it has fallen a height $\frac{h}{2}$, it will possess

(a) only potential energy
(b) only kinetic energy
(c) half potential and half kinetic energy
(d) more kinetic and less potential energy

Q.

A body of mass 3 kg is dropped from a height of 1m. The K.E of the body before touching the ground is: ......

Q.

When an object falls freely towards the earth, then its total energy :

(a) increases

(b) decreases

(c) remains constant

(d) first increases and then decreases

Q.

What is the total mechanical energy of an object falling from a height?

Q.

How can a body move with both potential and kinetic energy at the same time ? Give some examples . Please explain in easy way .

Q.

When the displacement is zero, the work done is zero.

1. True
2. False

Q. According to the law of conservation of energy:

1. Energy in the universe is constant.
2. Energy in the universe is reducing.
3. Energy in the universe is increasing.
4. Energy in the universe is zero.

Q. An Object is thrown vertically upwards with velocity of 20 m/s. At what height will its kinetic energy and potential energy be equal ? $(g=10m/s^2)$

1. $10m$
2. $20m$
3. $15m$
4. $5m$

Q.

Give one example, where sound energy changes into electrical energy.

Q.

When energy changes from one form to another, the energy that disappears from one form, reappears in an exactly equivalent amount in other forms.

1. False

2. True

Q.

Name the energy transfer which occurs when :

(a) an electric bell rings

(b) someone speaks into a microphone

(c) there is a picture on a television screen

(d) a torch is on

Q.

When an object falls freely towards earth, then its total energy remains constant.

1. True
2. False

Q.

The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?

Q.

A ball falls to the ground as shown below :

(a) What is the kinetic energy of ball when it hits the ground ?

(b) What is the potential energy of ball at B ?

(c) Which law you have made use of in answering this question ?

Q.

A microphone converts :

(a) electric energy into sound energy in ordinary telephone

(b) microwave energy into sound energy in a mobile phone

(c) sound energy into mechanical energy in a stereo system

(d) sound energy into electrical energy in public address system

Q.

Ten liter of water per second is lifted from a well through $10m$ and delivered with a velocity of $10m{s}^{-1}$ . If $g=10m{s}^{-2}$, then the power of the motor is

1. $1kW$

2. $1.5kW$

3. $2kW$

4. $2.5kW$