A spring balance is attached to the ceiling of a lift

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/s2, the reading of the spring balance will be

  1. 15 N
  2. 24 N
  3. 49 N
  4. 74 N

Answer

When lift is stationary, 

W1 = mg

When the lift descends with acceleration a,

W2 = m(g – a)

W2/W1 = (g – a)/g

= (9.8 - 5)/9.8 = 4.8/9.8

W2 = W1 x (4.8/9.8)

= 49 x (4.8/9.8)

= 24 N

The correct option is B.