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

Question

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) 24 N (B) 74 N (C) 15 N (D) 49 N

Tardigrade Admin · Accepted Answer

When lift is stationary, W1 = mg When the lift descends with acceleration a , W2 = m (g - a) ∴ (W2/W1) = (m(g - a)/mg) = (9.8 - 5/9.8) = (4.8/9.8) or W2 = W1 × (4.8/9.8) = (49 × 4.8/9.8) = 24 N

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

24 N

74 N

15 N

49 N

When lift is stationary, $W_{1} = m g$
When the lift descends with acceleration $a$ ,
$W_{2} = m (g - a)$
$∴ \frac{W _{2}}{W _{1}} = \frac{m ( g - a )}{m g} = \frac{9.8 - 5}{9.8} = \frac{4.8}{9.8}$
or $W_{2} = W_{1} \times \frac{4.8}{9.8} = \frac{49 \times 4.8}{9.8} = 24 N$

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 5ms−2, the reading of the spring balance will be