HOTS Questions: Work & Energy - Class 9 MCQ

When a body moves on a circular path. The force that acts on the revolving body towards the center is called centripetal force. As the force acts as right angle to the direction of motion, so work done is 0.

In physics, a work is said to be done when there is some displacement on the body on which force is applied. Work done is +ve when the body is displaced in direction of applied force.

Potential Energy of a body = mgh, hence the potential energy is maximum when you are standing, given that acceleration due to gravity and mass remain constant.

According to the law of conservation of energy, energy neither be created nor be destroyed, it can be transformed from one form to another. So, all the statements are true.

Work done when a body moves at an angle to the direction of force is W=Fcosϕ×s. The value of Cos is maximum for 0⁰. So, work done will be maximum for this angel.

One Giga watt is equal to 10⁹ watt or 10⁶ kilowatt. The rate of doing work is called as power. Hence both statements are correct.

An aeroplane flying at an altitude possesses both kinetic energy and potential energy. Kinetic energy is due to mass and velocity and potential energy is due to mass and height.

Initial velocity (u)= 0, final velocity (v) = 

1 kwH = 1000 W×60×60 s = 3600000J = 3.6 × 10⁶  J. one watt is equal to one joule per second.

Power of lamp = 100w = 100/1000 = 0.1Kw, time= 5 hrs. Electrical energy = power×timepower×time, E = 0.1kw×5h = 0.5 kw–h. = 0.5 unit.

The potential energy of a freely falling object decreases progressively due to decrease in height. Kinetic energy is converted into heat and sound energy when a freely falling object on reaching the ground. Work is done only when change in position occurs.

The total energy of the system is always conserved. It is just transformed from one form to other form. Mechanical energy of a system is not conserved. It is converted into other form of energy.

1 watt second (W.S) = 1J/s×s= 1 joule.

No work is done in reading a book, pulling wall of house and walking on a level road with book on his head as there is no change in the position of object on which force is applied. Stretching string causes displacement, so it is a work.

When you compress a coil spring you do work on it. The elastic potential energy increases.

1 unit (Kw-H) = 3.6×10⁶ joule. Therefore, 250 units = 250×3.6×10⁶joule
= 9×10⁸ Joule.

It is bromine as it has boiling point of 58.78 and has -7.2 melting point.

Potential energy of a spring increases when it is in the state of expansion and compression. Elastic potential energy increases with compression and gravitational potential energy increases on expansion.

The gravitational force of the earth on a satellite along a circular path is O as gravitational force of earth acts on right angle which is O for cos.

Potential energy = mgh, here, RE = 9800 j. mass = 50kg, g = 9.8m/s². Therefore, 9800 = 50 x 9.8 x h, h= 9800/50 x 9.8 = 20m. 

The kinetic energy of a freely falling object which eventually stops on reaching the ground changes into heat and sound energy.

Momentum = mass x velocity, velocity = momentum/ mass = 16/2 = 8m/s. Kinetic energy = ½ mv². K.E = ½ x2 x 82 = 64 J.

We know that, joule, newton metre and kilowatt hour are the units of energy and the kilowatt is the unit of power.