Question

a 70kg bicyclist (including the bicycle) is pedaling right with a constant speed despite experiencing a 40n drag. neglect any friction impeding her motion.
how many forces are acting on the bicyclist?
what is the magnitude of the net force on the bicyclist?
how much force is her pedaling generating?

Explanation:

Sub - question 1: How many forces are acting on the bicyclist?

To determine the number of forces, we consider the forces acting on the bicyclist. There is the gravitational force (weight) pulling down, the normal force from the ground pushing up, the drag force opposing the motion (40N to the left), and the pedaling force (thrust) propelling the bicyclist to the right. So we identify these four forces: gravity, normal force, drag force, and pedaling force.

Step 1: Recall Newton's first law

Newton's first law states that an object moving with a constant velocity (constant speed in a straight line) has a net force of zero acting on it. The bicyclist is moving with a constant speed, so the net force should be zero.

Step 1: Analyze the horizontal forces

In the horizontal direction, there are two forces: the drag force ($F_{drag}= 40N$) to the left and the pedaling force ($F_{pedal}$) to the right. Since the net force is zero (from part 2), the sum of horizontal forces must be zero. So $F_{pedal}-F_{drag}=0$.

Step 2: Solve for the pedaling force

Substitute $F_{drag} = 40N$ into the equation $F_{pedal}-F_{drag}=0$. We get $F_{pedal}=F_{drag}=40N$.

Answer:

4

Sub - question 2: What is the magnitude of the net force on the bicyclist?