Question 1 :
Power is defined as the rate of doing work. The SI unit of power is watt. 1 W = 1 J/s.

Question 2 :
A lamp consumes 1000 J of electrical energy in 10 s. What is its power?

Question 3 :
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy?

Question 4 :
An automobile engine propels a 1000 kg car along a levelled road at a speed of $36 kmh^{–1}$. Find the power if the opposing frictional force is 100 N.

Question 5 :
A porter lifts a luggage of 15 kg from the ground and puts it on his head 1.5 m above the ground. Calculate the work done by him on the luggage.

Question 6 :
The energy possessed by a body due to its change in position or shape is called the potential energy.

Question 7 :
Write an expression for the work done when a force is acting on an object in the direction of its displacement.

Question 8 :
Can there be displacement of an object in the absence of any force acting on it?

Question 9 :
The sum of the potential energy and kinetic energy of the object would be the same at all points. That is, potential energy + kinetic energy = constant.

Question 10 :
A mass of 10 kg is at a point A on a table. It is moved to a point B. If the line joining A and B is horizontal, what is the work done on the object by the gravitational force?

Question 11 :
A ball is dropped from a height of 10 m. If the energy of the ball reduces by 40% after striking the ground, how much high can the ball bounce back? $(g = 10 m s^{–2})$

Question 12 :
A body is falling from a height h. After it has fallen a height $\frac{h}{2}$ , it will possess

Question 13 :
<img style='object-fit:contain' src='https://teachmint.storage.googleapis.com/question_assets/cbse_ncert/61b1d2e1f59b460d7261f64b.png' /> In the above fig. A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force. Let us take it that the force acts on the object through the displacement. What is the work done in this case?

Question 16 :
The Jog Falls in Karnataka state are nearly 20 m high. 2000 tonnes of water falls from it in a minute. Calculate the equivalent power if all this energy can be utilized? $(g = 10 ms^{–2})$

Question 17 :
The energy used in one hour at the rate of 1kW is called 1 kW h. TRUE OR FALSE?

Question 18 :
Can any object have mechanical energy even if its momentum is zero?

Question 19 :
<img style='object-fit:contain' src='https://teachmint.storage.googleapis.com/question_assets/cbse_ncert/61b1d2f2f59b460d7261f662.PNG' /> The above image shows, A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force shown in figure. Let us take it that the force acts on the object through the displacement. What is the work done in this case?

Question 20 :
<img style='object-fit:contain' src='https://teachmint.storage.googleapis.com/question_assets/cbse_ncert/61b1d2e1f59b460d7261f64a.png' /> Look at the above image. In each of the following a force, F is acting on an object of mass, m. The direction of displacement is from west to east shown by the longer arrow. Observe the diagrams carefully and state whether the work done by the force is negative, positive or zero resctively.

Question 22 :
Energy exists in nature in several forms such as kinetic energy, potential energy, heat energy, chemical energy etc. The sum of the kinetic and potential energies of an object is called its mechanical energy.

Question 23 :
A battery lights a bulb. Describe the energy changes involved in the process.

Question 24 :
An object of mass 12 kg is at a certain height above the ground. If the potential energy of the object is 480 J, find the height at which the object is with respect to the ground. Given, g = 10 m $s^{-2}$.

Question 25 :
What is the work done by the force of gravity on a satellite moving round the earth?

Question 26 :
A lamp consumes 1000 J of electrical energy in 10 s. What is its power?

Question 27 :
Find the energy in kW h consumed in 10 hours by four devices of power 500 W each.

Question 29 :
The kinetic energy of a body moving with a certain velocity is ________ to the work done on it to make it acquire that velocity.

Question 30 :
The kinetic energy of an object of mass, m moving with a velocity of 5 m $s^{-1}$ is 25 J. What will be its kinetic energy when its velocity is doubled? What will be its kinetic energy when its velocity is increased three times?