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Question

A spring balance is attached to the ceiling of a lift. A man hangs his bag on the spring and the balance reads 49 N, when the lift is stationary. If the lift moves downward with an acceleration of 5 m/s2, the reading of the spring balance would be

A
24 N
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B
74 N
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C
15 N
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D
49 N
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Solution

The correct option is A 24 N
When the lift is stationary, the spring force Fs in spring balance will be equal to the weight of bag.

Fs=W=49 N

or, mg=49m(9.8)=49

m=499.8=5 kg

When lift is accelerating downwards, the acceleration of bag will be same as that of lift.

Applying Newton's 2nd law of motion,

mgFs = ma

49Fs=5×5

Fs=4925=24 N

Thus, new reading of spring balance will be 24 N.

Why this question ?Tip: Spring balance measures theweight of a body based on the springforce recorded by it.

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