A block with the mass of 50 kg is on the floor of an elevator that is accelerati

Question

A block with the mass of 50 kg is on the floor of an elevator that is accelerating upward at 3 m/s^2. It requires a horizontal force of 300 N to start the block moving across the floor of the elevator. Find the coefficient of static friction between the block and the floor of the elevator. A 40 kg crate is initially at rest on the floor of a 2000 kg truck. The coefficient of static friction between the crate and the floor of the truck is 0.3 and the coefficient of kinetic friction is 0.2. If the truck is moving accelerating forward at 2.2 m/s^2 find the friction force acting on the crate. If the truck is moving decelerating (slowing down) forward at 3.4 m/s^2 find the friction force acting on the crate.

Explanation / Answer

a) Friction = 300 N = u * 50* (9.8+3) => u = 0.46875 ------------Answer

b) Max static friction = 40*9.8*0.3 = 117.6 N

When accelerating forward at 2.2 m/s2, pssudo force = 40*2.2 = 88 N which will be balanced by static friction.

Thus friction acting = 88 N --------------------Answer

If decelerating, pseudo force = 40*3.4 = 136 N. However max friction = 117.6 N.

Thus kinetic friction will act, Friction acting = 78.4 N ----------------Answer

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