A 40-kg box is moving on the floor. The coefficient of static friction between the box and the floor is
0.650, and the coefficient of kinetic friction is 0.500. If the pulling force is applied horizontally, what is
the magnitude of the force to maintain a constant velocity motion?
Alex Gallenberger
Because we are finding the force to maintain motion, we can ignore the static friction coefficient. When dealing with friction,
Force = (Coef. Frict.)*(normal force)
Since the box is on a horizontal surface, and the force applied is also horizontal, our normal force is the same as the weight. To find weight,
Force = mass*acceleration
In this case, our acceleration is that of gravity, 9.81m/s^2
Force = (40kg)*(9.81m/s^2)
Force = 392.4 N
This is the normal force
We then plug this into our friction equation.
Force = (.500)*(392.4N)
Force = 196.2N
oldschool
Use the kinetic friction 0.5 For constant velocity, Fnet = 0 = 40*g*0.5 - F => F = 196N