Question

An elevator is moving down with a constant
acceleration of 1 ms. How much lighter
does an 80 kg man feel riding the elevator?
(A) 60 N
(B) 40 N
(C) 80 N
(D) 20 N​

Answer 1

Explanation:

1. as the lift is going downward with constant acceleration so a=1 g=0
2. R= m(g-a)

= 80(0-(-1))

= 80× 1

= 80N

Answer 2

Answer:

When the elevator is moving down with a constant acceleration of 1 ms it has 80 N lighter does an 80 kg man feel riding the elevator.

Explanation:

Net force = weight of man (downward) + Psuedo force (upward)

= mg + m(-a)

= m(g - a)

= 80 × (10 - 1)

= 80 × 9 = 720 N

Hence, normal reaction acting on a man = 720N

But the actual weight of man = mg = 80 × 10 = 800N

Now , 800 - 720 = 80 N .