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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 2ms2 and then comes down with an acceleration of 2ms2 , is

A
120N
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B
240N
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C
480N
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D
720N
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Solution

Step 1: Given

Mass(mmm)= 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(ggg) = 10 m/s2m/s^2m/s2

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

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

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(ga)

Change in weight = W2−W1=m(au+ad)W_{2}-W_{1}=m(a_u+a_d)W2W1=m(au+ad) = 4×m.

change in weight $= 4×60 = 240 N$

Hence, the change in the apparent weight of the person is 240N240N240N.

Thus, option C is correct.


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