Question

A 96lb boy is standing in an elevator.Find the force on the boy's feet when the elevator(a)stands still(b)moves downward at a constant velocity of 3 ft/d(c)accelerates downward with an acceleration of 4.0 ft/s2, and(d)accelerates upward with an acceleration of 4.0ft/s2​

Answer 1

Answer:

Explanation:

a ) When the elevator is at rest

R = mg

R =  force on the boy's feet = 96 x 32

= 3072 unit .

b ) When the elevator moves with uniform velocity , net force on the boy = 0

R = mg

force on the boy's feet = 96 x 32

= 3072 unit

c ) When the elevator moves with acceleration a  downwards

Reaction force R = mg - ma

= m ( g-a )

= 96 ( 9.8 - 4 )

= 556.8 unit

d )

When the elevator moves with acceleration a  upwards

Reaction force R = mg + ma

= m ( g+a )

= 96 ( 9.8 + 4 )

= 1324.8  poundal

Answer 2

Answer:

Explanation:

mass of boy, m = 96 lb

acceleration due to gravity, g = 32 ft/s²

(a) When the elevator is stands still

Force, F =  m g

F = 96 x 32 = 3072 pounds

(b) When the elevator moves with constant velocity

F = mg = 3072 pounds

(c) When the elevator moves downwards with constant acceleration

F = mg - ma

F = 96 ( 32 - 4)

F = 2688 pounds

(d)

When the elevator moves upwards with constant acceleration

F = mg + ma

F = 96 ( 32 + 4)

F = 3456 pounds