Q. A 60 kg man stands on a spring scale in a lift. At some instant he finds that the scale reading has changed from 60 kg to 50 kg for a while and then comes again to 60 kg mark. What should he conclude?
A) The lift was in constant motion upwards
B) The lift was in constant motion downwards
C) The lift while in motion suddenly stopped
D) The lift while in motion upwards suddenly stopped
Explanation
(d) When lift falls with acceleration $(a)$or rises with retardation $( - a),$ then a person apparently loses weight.
$R - mg = - ma$
$\Longrightarrow \ \ \ R = m(g - a)$
In the given case scale reading changes from 60 kg to 50 kg for a while and then comes back to 60 kg mark. It happens while the lift in motion upwards suddenly stops.
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Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.