Answer to Question #247718 in Mechanics | Relativity for Sajida

Question

A child of mass 30 kg travels in a lift calculate the force exerted on the child by the floor of the lift when the lift moves 1.downward with an acceleration of 1 metre per second 2.upward with an acceleration of 1 metre per second what is the weight of the child when the lift falls freely. g =10ms^-2

Answer 1

1.

$F=mg-ma=30(10-1)=270$ N

2.

$F=mg+ma=30(10+1)=330$ N

When the lift falls freely, a=g, so:

$F=mg-mg=0$

This means that the weight of the child is zero.