Question

A person of mass 50 kg stands on a weighing scale on a lift. If the lift is ascending upwards with a uniform acceleration of $9 \mathrm {~m} \mathrm {~s} ^ { - 2 }$ , what would be the reading of the weighing scale? (Take $\mathrm { g } = 10 \mathrm {~m} \mathrm {~s} ^ { - 2 }$ )

• A. 50 kg
• B. 60 kg
• C. 95 kg
• D. 100 kg

Answer 1

Answer: (C)

95 kg

Answer 2

The reading on the scale is a measure of the force on the floor by the person. By the Newton’s third law this is equal and opposite to the normal force N on the person by the floor

$\therefore$When the lift is ascending upwards with a acceleration of $9 m s ^ { - 2 }$ then

$N - 50 \times 10 = 50 \times 9$

Or $N = 50 \times 10 + 50 \times 9 = 50 ( 10 + 9 ) = 950 N$

$\therefore$ The reading of weight machine is 95 kg