Question

A 70kg bicyclist (including the bicycle) is pedaling right with a constant speed despite experiencing a 60N drag. Neglect any friction impeding her motion. How many forces are acting on the bicyclist?

a) 2 forces
b) 3 forces
c) 4 forces
d) 5 forces

Answer 1

The bicyclist is subject to three forces: the drag force of 60N, the gravitational force (weight), and the pedaling force, which is equal and opposite to the drag force, thus allowing her to maintain a constant speed.

Step-by-step explanation:

The question involves a 70kg bicyclist pedaling with a constant speed and experiencing a 60N drag force. If we are to consider the forces acting on the bicyclist, and we are neglecting any friction, we should still consider the following forces: the drag force (also known as air resistance), the force of gravity (weight of the bicyclist and bicycle), the normal force from the ground, and the pedaling force that the cyclist applies to maintain constant speed. Hence, the answer is (b) 3 forces since the pedaling force and the normal force can be considered as one force exerted by the cyclist on the ground (and by Newton's third law, the ground exerts an equal and opposite force).

If the drag force is 60N and the bicyclist maintains a constant speed, then the force that the bicyclist must exert through pedaling must be equal and opposite to the drag force. Together with the weight and the normal force (which are also equal and opposite), these comprise the three forces acting on the cyclist.