Question

A 28.0-kg block is initially at rest on a horizontal surface. A horizontal force of 73.0 N is required to set the block in motion, after which a horizontal force of 55.0 N is required to keep the block moving with constant speed.

(a) Find the coefficient of static friction between the block and the surface.


(b) Find the coefficient of kinetic friction between the block and the surface.

Answer 1

Answer 2

(a) To find the coefficient of static friction (μs) between the block and the surface, we use the formula:

μs = (Force required to set the block in motion) / (Normal force)

The normal force (N) is the force exerted by the surface on the block, which is equal in magnitude and opposite in direction to the force of gravity acting on the block. The normal force can be calculated using the formula:

Normal force (N) = Mass of the block (m) × Acceleration due to gravity (g)

where Mass of the block (m) = 28.0 kg Acceleration due to gravity (g) = 9.8 m/s²

Given data: Force required to set the block in motion = 73.0 N

Now, let's calculate the coefficient of static friction (μs):

μs = 73.0 N / (28.0 kg × 9.8 m/s²) μs ≈ 0.265

(b) To find the coefficient of kinetic friction (μk) between the block and the surface, we use the formula:

μk = (Force required to keep the block moving) / (Normal force)

Given data: Force required to keep the block moving = 55.0 N

The normal force (N) is the same as calculated in part (a).

Now, let's calculate the coefficient of kinetic friction (μk):

μk = 55.0 N / (28.0 kg × 9.8 m/s²) μk ≈ 0.200

So, the coefficients of static friction and kinetic friction between the block and the surface are approximately 0.265 and 0.200, respectively.