Answer to Question #104304 in Classical Mechanics for Augustine francis

Question

1. Jim's mass is m = 62 kg. He is standing in a lift, with no motion relative to the lift.

a) The lift accelerates upwards at 2.0 m.s^-2. What is the magnitude of the force the floor of the lift exerts on Jim?
b) Later, the lift accelerates downwards at 2.0 m.s^-2. What is the magnitude of the force the floor of the lift exerts on Jim?
c) Just suppose that the lift were to accelerate downwards at 10.0 m.s^-2. What force would the floor of the lift exert on Jim?

Answer 1

a)

$$N_1=m(a+g)=62(2+9.8)=730\ N$$

b)

$$N_2=m(g-a)=62(9.8-2)=480\ N$$

c)

$$N_3=0\ N$$

For $g\leq a$ there is no force between floor and Jim. He would accelerate upwards relative lift.