- #1

MatinSAR

- 597

- 182

- Homework Statement
- Imagine you push a block against wall of an elevator that is accelerating downward. What is the minimum force you should apply to prevent block's free fall?

- Relevant Equations
- N's laws.

Easier case: Elevator is at rest.

We need to prevent box from free fall so friction should be bigger than "mg".(And they can be equal)

When we push with force F we know that the maximum static friction is ##u_sF##.

"mg" should be smaller than ##u_sF## or should be equal to it so the minimum value for ##F## is : ##F=\frac {mg} {u_s}##. Am I right?!

But here the elevator is accelerating downward ... I can guess that here F is equal to ##\frac {mg+ma} {u_s}## ... Is my guess correct?! Is there any good reason for it?!