A bike rolls across the ground with a force of 100 N and friction acts against the wheels with a force of 15 N per wheel. What is the net force acting on the bike?

Question

Quizplus · Accepted Answer

There are two forces in the question above: the applied force and the friction force. However, friction acts with a force of 15 N on each of the two wheels. Thus, friction acts with a total force of 30 N. Since it directly opposes the applied force, it has an opposite sign.
Net force = Applied force + Friction force
Net force = 100 N + (-15 N) + (-15 N)
Net force = 70 N
Remember that friction is working against the applied force (in the opposite direction), so it is a negative value.

A Bike Rolls Across the Ground with a Force of 100