Question

a kg bicyclist (including the bicycle) is pedaling right with a constant speed of 10m/s despite experiencing a 10n drag. neglect any friction impeding the motion.
how many forces are acting on the bicyclist?
are the forces on the bicyclist balanced?
how much force is the bicyclist generating through her pedaling?
unit
how much power is she expending?
unit

Explanation:

Step1: Identify forces

There is gravitational force pulling down, normal force pushing up, drag force opposing motion, and the force from pedaling. So 4 forces.

Step2: Analyze force balance

Since the speed is constant, acceleration \(a = 0\). According to Newton's second - law \(F_{net}=ma\), when \(a = 0\), \(F_{net}=0\), so the forces are balanced.

Step3: Calculate pedaling force

The drag force \(F_d=10N\). For the forces to be balanced in the horizontal direction, the force from pedaling \(F_p\) must equal the drag force. So \(F_p = 10N\).

Step4: Calculate power

The formula for power is \(P = Fv\). Here \(F = F_p=10N\) and \(v = 10m/s\). So \(P=10N\times10m/s = 100W\).

Answer:

How many forces are acting on the bicyclist? 4
Are the forces on the bicyclist balanced? Yes
How much force is the bicyclist generating through her pedaling? 10 N
How much power is she expending? 100 W