Q: A 60 kg man is inside a lift which is moving up with an acceleration of 2.45 ms^{2} . The apparent percentage change in his weight is,(g = 9.8 m/s^{2})

(a) 20%

(b) 22.5%

(c) 50%

(d) 75%

Ans: (b)

Sol:

$ \displaystyle R – Mg = M a$

$ \displaystyle R = M(g + a ) $

R = 60(9.8 + 2.45)

R = 735 N

Percentage change in weight is

$ \displaystyle = \frac{R -Mg}{Mg}\times 100 $

$ \displaystyle = \frac{735-600}{600}\times 100 $

= 22.5 %