Question 1.

A body weighing 80 N stands in an elevator that is about to move. The force exerted by the floor on the body as the elevator moves upwards with an acceleration of 5 ms^-2 is ? (g = 10 ms^-2) 

Solution:

The net force on the body is given as follows: 

R - mg = ma

Where R is the reaction, or the vertical upward force exerted by the floor of the elevator on the body; m is the mass of the body, a is acceleration with which the body moves upwards, mg is the weight of the body.

Therefore,

Since weight of the body mg = 80 N

m = 80/10 = 8

mass of body = 8 kg

 Substituting known values in R - mg = ma, we have

 R - 80 = 8 x 5

R  = 40 + 80

    = 120 N

 The force exerted on the body by the floor is 120 Newtons.