Q. A motor drives a body along a straight line with a constant force. The power $P$ developed by the motor must vary with time $t$ as shown in figure
A) [image:6_image27.emf]
B) [image:6_image28.emf]
C) [image:6_image29.emf]
D) [image:6_image30.emf]
Explanation
(a) We know that $P = F \times v = F \times \frac{L}{T}$
As $F = \lbrack MLT^{- 2}\rbrack =$ constant
$\therefore\ L \propto T^{2}$
$\therefore\ P = F \times \frac{L}{T} = F \times \frac{T^{2}}{T} = F \times T$
or $P \propto T$
Choice (a) is correct
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.