1. (a) Give one example, where a body is in motion, yet it possesses no energy.
(b) Is the energy a scalar or a vector quantity ?
(c) What happens to the potential energy of a body, if its (1) height is doubled, (ii) mass is increased
by three times, (iii) the body is taken on the surface of the Moon?
Answers
Answer:
(a) For example, when you pedal a bicycle and continue it to pedal the same way for a certain time, you get a constant velocity. In absence of friction it is not used and consumed energy.
(b) Mass and energy are scalar quantities, while momentum is a vector quantity. This results in a coupled set of equations, called the Navier-Stokes equations, which describe how fluids behave when subjected to external forces.
(c) (i) Since the gravitational potential energy of an object is directly proportional to its height above the zero position, a doubling of the height will result in a doubling of the gravitational potential energy. A tripling of the height will result in a tripling of the gravitational potential energy.
(ii) Gravitational potential energy may be converted to other forms of energy, such as kinetic energy. If we release the mass, gravitational force will do an amount of work equal to mgh on it, thereby increasing its kinetic energy by that same amount (by the work-energy theorem).
(iii) The new potential increases by 4 times of the original. b) When the body is taken on the surface of Moon. The new potential decreases by 1/6 times of the original.