can someone please help me with this?

Question

A 3.40 kg box is sliding across the horizontal floor of an elevator. The coefficient of kinetic friction between the box and the floor is 0.410. Determine the kinetic frictional force that acts on the box for each of the following cases.
(a) the elevator is stationary
___N
(b) the elevator is accelerating upward with an acceleration whose magnitude is 1.40 m/s2
___N
(c) the elevator is accelerating downward with an acceleration whose magnitude is 1.40 m/s2
___N

Answer 1

The basic equation for frictional force is N x C, where
N is the normal force, and
C is the coefficient of friction

You know C so the problem reduces to finding N in the three cases.

The general rule for acceleration is: F = M x A, where
F is the net force,
M is the mass, and
A is the acceleration

You have a known constant mass and three acceleration values so you can compute the three net forces.

The net force is the sum of all the forces acting on the object. In this case, we are interested only in the vertical forces so we can ignore the frictional force.

So, net force = N + W, where
N is the normal force as above (the force the floor exerts on the box), and
W is the force of gravity on the box.

Since you have the mass of the box you can compute W, the force of gravity on the box.

Then you can use the three net force values to compute the three normal forces. (Be careful with the signs here.)

With that information, you can compute the frictional force.