A body weighing 80N stands in an elevator that ... - JAMB Physics 2002 Question

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

40 N

80 N

120 N

160 N

correct option: d

Let M = mass of elevator

m = mass of the body

g = acceleration of free fall

a = upward acceleration of the elevator (5m/s^s)

when the elevator is at rest, the force it exerts on the body is equal to the weight of the body. And from Newtons third law, Mg = mg

However as the elevator ascends the net upward force F = Mg - mg = (M + m)a.

Thus, if the weight of the body = 80 N, then 88 its mass, m = 80/10 = 8kg.

Therefore M x 10 - 8 x 10 = (M + 8) 5

10M - 80 = 5M + 40

10M - 5M = 40 x 80

5M = 120 => M = 120/5 = 24kg.

Thus, net upward force = force exerted by the elevator floor on the body = (M x m)a

              = (24 x 8) x5<br />

              = 32 x 5<br />

              = 160 N

Please share this, thanks:

#JAMB #JAMB