# How do I calculate the magnitude of initial acceleration?

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1. Nov 22, 2015

### sarahin3d

1. The problem statement, all variables and given/known data
A system consists of a bicycle and a cyclist travelling at a constant velocity along a horizontal road.

The total resistive force acting on the system in 4.0N and its speed is 8.0 m/s. Calculate the useful power output of the cyclist.

The cyclist stops pedalling and the system comes to rest. The total mass of the system is 70kg.
i) Calculate the magnitude of the initial acceleration of the system.

2. Relevant equations

P=Fv
s=ut+1/2at

3. The attempt at a solution

Alright so I used P=Fv to find the useful power output and I think I got the answer to that right.
P=Fv
P=(40)(8)
P=320 W

I don't know how to calculate the magnitude of the intial acceleration of the system. I would think that since the velocity is constant that the acceleration would have a magnitude of 0. This question is a 2 mark problem so I don't think that that answer would be right.

2. Nov 22, 2015

### Staff: Mentor

Hi sarahin3d, welcome to Physics Forums.

The velocity was constant while he was peddling. But for this part of the question it says that the cyclist stops peddling.

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