A force of 39.0 N accelerates a 5.0-kg block at 6.3 m/s2 along a horizontal surface.

(a) How large is the frictional force? N
(b) What is the coefficient of friction?

Hello Fender

The sum of the forces on the object in the direction of movement equals the mass times the acceleration.

What is the sum of the forces in the x direction? The applied force (F) in the positive direction and the friction force (Ff) in the negative direction.

sum of forces = F - Ff = m*a

Solve for Ff

Ff = F - m*a

Ff = 38 .0 N - (5 kg * 6.3 m/s^2)

Ff = 7.5 N (in the minus x direction)

B) Ff = u * N = u * m * g

I am using (u) for coefficient of friction, but it is kinetic, not static.

u = Ff / (m*g)

u = 7.5 N / (5 kg * 9.81 m/s^2)

u = 0.15

Good Luck