Question

The work done by a particle moving with a velocity of $0.7\, c$ (where c is the velocity of light) in empty space free of electromagnetic field and far away from all matter is:

• A. positive
• B. negative
• C. zero
• D. infinite

Answer 1

Answer: (C)

zero

Answer 2

Acceleration of the particle $a=\frac{dv}{dt}=\frac{d}{dt}(0.7c)=0$ ( $\because$ $c=$ constant) Force on the particle $F=ma=0$ Thus, work done by a particle will be zero.