CBSE Class:IX Work Power and Energy Questions and Solution

Q.1. Can any object have mechanical energy even if its momentum is zero? Explain.

Yes, mechanical energy comprises of both potential energy and kinetic energy. Zero momentum means that velocity is zero. Hence, there it no kinetic energy but the object may possess potential energy.

Q.2. The potential energy of a body is 39600J. How high is the body if its mass is 20kg?

The potential energy of a body = mgh

h = PE/mg = 39600j/20kg x9.8m/s²=198m

Q.3. A force of 20 N displaces a body through a distance of 1 m at an angle of 60° from its own direction. Calculate the amount of work done.

Here, force F = 20 N, displacement, s = 1 m. Angle between force and displacement 60°.

Work done,W =Fscos0 =20 X 1 X cos60°=20X 1 X 1/2 = 10J.

A man of 50 kg jumps up to a height of 1.2 m. What is his potential energy at the highest point?

The potential energy of man = mgh = = 50 + 10 X 1.2 J = 600 J

Q.4. How much work is done by a force of 10 N in moving an object through a distance of 4 m in the direction of the force.

Work done Force x Displacement =F.s = (10 N) x (4 rn) = 40 joule or 40J.  
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IX Physics Chapter: Work Power and Energy

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