Question

A man enters a lift at the 20th floor of a 40 storey building and stands on a weighing scale which shows a reading of 600 N. When the lift door is closed, the scales read720 N for the first 5 seconds, 600 N for the next 20 seconds and then 480 N for the next 5 seconds after which the lift door is opened. Which of the following statements is correct?​

Answer 1

Answer:

Mass of the man m=40kg

Acceleration of lift in upward direction a=2m/s

2

Let the weight shown by machine be N.

Equation of motion for the body : ma=N−mg

We get N=m(a+g)

∴ N=(40)(2+10)=480 N

Thus weight of the man recorded by machine W

′

=

g

N

∴ W

′

=

10

480

=48 kg