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

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

show the wavelengths of a wave. show the crests of a wave.

force is mass*acceleration.

we have a very small mass: 11.4*0.001 kg

if we want 0.035n of force, we need an acceleration:

0.035 = 11.4*0.001*a

a = 0.035/(11.4*0.001) m/s^2