A 60 kg box is sliding across the horizontal floor of an...

A 6.0 kg box is sliding across the horizontal floor of an elevator. The coefficient of kinetic friction between the floor and the box is 0.360. Determine the frictional force that acts on the box when the elevator is a) stationary b) accelerating up with an acceleration whose magnitude is1.2 m/s2 and c) accelerating downward with an acceleration whose magnitude is 1.2 m/s2.

Transcript

00:01 Friction force is a force that tries to oppose the motion of an object and it is solved as the product of mew and n, where m is the coefficient of friction and is the normal force, which is the force that the surface exerts on an object that it supports.

00:14 In this problem, a 6 -kilogram block or box would slide across the horizontal floor of an elevator.

00:21 The coefficient of kinetic friction between the floor and the box is 0 .36.

00:25 We wish to find the frictional force that acts between the box and the elevator floor if the elevator is letter a stationary.

00:34 Letter b, accelerating upward at a rate of 1 .2 meters per second squared.

00:39 And letter c, accelerating downward at the rate of 1 .2 meters per second square.

00:43 So first is that let us draw the free body diagram of the box.

00:48 So we have the downward weight, the upward normal force, and the friction force.

00:55 Let's suppose that the box moves to the right so that friction force is acting on the left so when we take the net force on the box in the direction of the motion of the elevator which is going up or down then we have m times a that's your net force and that's equal to the normal force minus the weight taking upward as the positive direction so here our goal is to express though n your in terms of the acceleration and the weight.

01:29 So we have m a plus w.

01:32 But w is equal to mass times the acceleration due to gravity g.

01:39 So we have n equals.

01:41 Take out the mass.

01:42 We have a plus g...

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