Question

Identify the wrong statement among the following. Rewrite them by making necessary corrections.
a) Work and energy have different units.
b) When an aeroplane takes off, the work done by its weight is positive.
c) The potential energy of spring increases when it is extended and decreases when it is compressed.
d) If the work done by external forces on a system is negative then the energy of the system decreases.
e) When a body is falling freely from a height, its kinetic energy remains constant.
f) The unit of power is watt.

Answer 1

(a) False :
Work and Energy has same units i.e. Joules.

(b) False :
When an aeroplane takes off, it displaces in upward direction but gravity force acts in downward direction.
=> Work done by gravity force here is negative .

(c) False :
The potential energy of a spring is is always increases whether it compresses or extended .
Work done by external Force to compress or extend acts opposite to the spring force which is stored as potential energy.

(d) True :
When work done by external Force is negative then Mechanical energy of the system decreases when compared to zero / Positive work done on the system.

(e) False :
When a body is falling from some height ,then speed of body increases due to gravitational force, hence Kinetic energy increases.

(f) True
The SI unit of power is Watt.