Q. A spring balance is attached to the ceiling of a lift. A man hangs his bag on the spring and the spring reads $49\ N$, when the lift is stationary. If the lift moves downward with an acceleration of $5\ m/s^{2}$, the reading of the spring balance will be
A) $49\ N$
B) $24\ N$
C) $74\ N$
D) $15\ N$
Explanation
(b) When the lift is stationary $W = mg$
$\Rightarrow 49 = m \times 9.8 \Rightarrow m = 5\ kg$
When the lift is moving downward with an acceleration
$R = m(9.8 - a) = 5\lbrack 9.8 - 5\rbrack = 24\ N$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.