Question

A person of mass 60 kg is in a lift. The change in the apparent weight of the person, when the lift moves up with an acceleration of $2m{s}^{-2}$ and then comes down with an acceleration of $2m{s}^{-2}$ , is

• A. 720N
• B. 120N
• C. 240N
• D. 480N

Answer 1

Answer: (C)

Step 1: Given

Mass($m$)= 60 kg

Acceleration of lift in upward direction(aua_uau​) = 2 m/s22 {m}/{s^2}2 m/s2

Acceleration of lift in downward direction(ada_dad​) = 2 m/s22 m/s^22 m/s2
Acceleration due to gravity($g$) = 10 m/s2m/s^2m/s2

Step 2: Formula used
Weight of a person when lift is moving up = $m(g+a)$

Weight of a person when lift is moving down = $m(g-a)$

Step 3: Finding the change in the apparent weight of the person

Weight of a person when lift is moving up W1=m(g+a)W_{1}=m(g+a)W1​=m(g+a)

Weight of a person when lift is moving down W2=m(g−a)W_{2}=m(g-a)W2​=m(g−a)

Change in weight = W2−W1=m(au+ad)W_{2}-W_{1}=m(a_u+a_d)W2​−W1​=m(au​+ad​) = 4$\times$m.

change in weight $= 4$\times$60 = 240 N$

Hence, the change in the apparent weight of the person is $240N$.

Thus, option C is correct.