# Homework Help: Centripetal Acceleration of bicyclist

1. Oct 6, 2007

### sylenteck0

1. The problem statement, all variables and given/known data
A bicyclist travels in a circle of radius 25.0m at a constant speed of 9.00 m/s. The bicycle-rider mass is 85.0 kg. Calculate the magnitudes of a) the force of friction on the bicycle from the road and b) the net force on the bicycle from the road.

2. Relevant equations
F=ma
m(v^2/r)

3. The attempt at a solution
I plugged in the numbers for the force formula and got 275.4 N, I'm assuming that's the net force as its the centripetal force.

Im unsure how to find the force of the friction however. Any suggestions? (On that note, did I confuse the two?

2. Oct 6, 2007

### Staff: Mentor

Start by listing all the forces acting on the bicycle: name them and indicate their direction.

You did calculate the net force (assuming your arithmetic is correct), but the question asks for the net force from the road, which is not the same thing.

3. Oct 6, 2007

### sylenteck0

Ah, so what I found was the force of the bicycle on the road?

So, the net force on the bicycle on the road would be the reactive force from gravity, making it 9.8 x 85.0 kg, right? (Which is 833N)

4. Oct 6, 2007

### Staff: Mentor

What you found was the net force on the bicycle due to all forces, not just from the road.

What forces does the road exert on the bicycle? (Consider vertical and horizontal forces separately.)

5. Oct 6, 2007

### sylenteck0

According to the answer sheet, the answers I got are correct, but I'll get on thinking about that :)

6. Oct 7, 2007

### Staff: Mentor

How did you answer the questions? You've shown your calculation of the net force on the bicycle. That is one of the answers, but which one?

That's the normal component of the force the road exerts on the bicycle, not the net force.

For your own clarity, I'd still recommend listing the forces acting on the bicycle and their direction.

Just curious what the answer sheet says.