Question

A boy of weight 60 kg wt is standing in a lift.If the lift begins to move up with a uniform speed 4.9 m/s the apparent weight of the boy is

Answer 1

Given:

• Weight of boy in stationary lift = 60 kgwt
• Lift moves up with uniform speed of 4.9 m/s.

To find:

• Apparent weight of boy ?

Calculation:

When a lift moves upwards with acceleration, any object in the lift experience pseudo force downwards, which increases the apparent weight of the object.

• But , the question clearly mentions that the lift is moving upwards with a uniform speed of 4.9 m/s.

This means that the boy will NOT EXPERIENCE ANY PSEUDO-FORCE !

• Hence, the apparent weight of the boy will be equal to the actual weight of the boy.

$\boxed{ \bf W_{app.} = W_{actual} = 60 \: kgwt}$

Answer 2

Given :

Weight of the boy - 60 kg-wt

Lift is moving with uniform velocity (v) = 4.9 m/sec

To Find :

The apparent weight of the boy in the lift.

Solution :

As the lift is moving with uniform velocity, acceleration = $\frac{dv}{dt}$ = 0

Hence, the boy doesn't experience any pseudo force,

so, Normal reaction = mg = the actual weight of the body = 60 kg-wt

∴ The apparent weight of the boy in the lift = 60 kg-wt.