How to calculate frictional force when kinetic friction involves
Answers
1) A worker in a stock room pushes a large cardboard box across the floor. The coefficient of kinetic friction is μk = 0.520. The box has a mass of 75.0 kg, and the worker is exerting a force of 400.0 Nforward. What is the magnitude of the force of friction, and what is the net force moving the box?
Answer: On a flat surface, the normal force on an object is η = mg. Using this, the formula can be used to find the force of friction:
Fk = μk η
Fk = μk mg
Fk = (0.520)(75.0 kg)(9.80 m/s2)
Fk = 382.2 kg∙m/s2
Fk = 382.2 N
The force of kinetic friction acting in the opposite direction as the motion of the box is 382.2 N. The net force acting on the box is the sum of forces. The two forces to consider are the force of kinetic friction acting in the opposite direction as the box's motion, and the force exerted by the worker, which is 400 N forward. If we define "forward" as the positive direction, the net force is:
Fnet=Fworker-Fk
Fnet=400.0 N-382.2N
Fnet = 17.8 N
The net force acting on the box is 17.8 N forward.