Olympiad Test: Work and Energy- 3 - Class 9 MCQ

P = 60 W

= 0.06 kW

Time, t = 6 h

Energy = power × time

= 0.06 kW × 6 h

= 0.36 kWh

= 0.36 ‘units’

Kinetic energy is mathematically defined as K.E = ½ mv²

Hence kinetic energy is directly proportional to the square of the velocity. Thus if we increase the speed of a motor by 6 times then the kinetic energy becomes 36 times.

= 10×10/2×0.02 = 2500 j = 2.5 kj

For worktop be done, there should be a motion of the body in the direction of the force applied.

So, the correct answer is B) the pull of a moving railway engine on its coaches.

Mg = 400 N, h = 2 m

∴ work done = P.E. = mgh = 800 Nm = 800J

one second. Thus, in1 minute or 60 seconds,

energy consumed is 100 J × 60

= 6000 J.

When a spring is at its natural length (i.e. neither stretched nor compressed), the potential energy of a spring will be minimum.

Hence, Kinetic energy is zero.