Question

During the motion of a lift, apparent weight of a body becomes half its actual weight when:-
(a) lift is moving down with acceleration ‘g’
(b) lift is moving up with acceleration ‘g’
(c) lift is moving down with uniform velocity 5 ms-1
(d) lift is moving up with uniform velocity 5 ms-1

Answer 1

Answer:

a=g/2 downwards

Explanation:

See the image for solutions

Answer 2

Correct  Question

During the motion of a lift, the apparent weight of a body becomes half its actual weight when:-

(a) lift is moving down with acceleration ‘$\frac{1}{2} g$’

(b) lift is moving up with acceleration ‘$\frac{1}{2} g$’

(c) lift is moving down with uniform velocity 5 ms-1

(d) lift is moving up with uniform velocity 5 ms-1

Answer:

During the motion of a lift, the  apparent weight of a body becomes half of  its actual weight when lift is moving down with acceleration ‘$\frac{1}{2} g$’ and option (a) is correct.

Explanation:

Given:

The apparent weight of a body becomes half its actual weight during the motion of a lift.

To Find:

Lift movement when the apparent weight of a body becomes half its actual weight.

Concept Used:

When the lift moves downwards with acceleration a. Then the net downward force on the body  can be expressed as :

mg - K = ma     ------  formula no.01.

Where,

m= mass of the body

g= gravitational acceleration

K= apparent weight

∴  The apparent weight, K = mg - ma = m (g - a)

Therefore, when a lift accelerates downwards, the apparent weight of the body inside it decreases.

Solution:

Let the mass of the body be m kg.

As given, the apparent weight of a body becomes half its actual weight during the motion of a lift.

The actual weight of the body =mg

The apparent weight of a body,K $=\frac{mg}{2}$

Applying formula no.01.

mg - K = ma  

$mg - K = ma \\mg-\frac{mg}{2} =ma\\\frac{mg}{2} =ma\\a=\frac{g}{2} \ m/s^{2}$

Thus, during the motion of a lift, the  apparent weight of a body becomes half of  its actual weight when lift is moving down with acceleration ‘$\frac{1}{2} g$’ and option (a) is correct.

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