# Calculating time from velocity and acceleration?

1. Apr 7, 2010

### robinfisichel

Simple? You would think so , see if you agree with my approach...

I have a car, I know its power at certain Rpm's and I know the magnitude of resitive forces.

So
1. I calculate the power loss due to resitive forces
2. I calculate the net power by subtracting this from motive power.
3. I calculate the velocity from the Rpm of the motor, through gearing down to wheel speed and then tangental velocity.
4. I calculate the net force by dividing by velocity.
5. Dividing by the mass gives me the max acceleration at a particular rpm.

Now i want to calculate how quickly i can accelerate from 0-30 m/s (for example) so using a=dv/dt and rearranging for dt = dv/a i should be able to calculate how long it takes to accelerate from a certain speed at a certain acceleration.

Would people agree with this approach

One problem with this is for this motor, and most other motors, the power at 0 rpm is zero, so i should probably use the torque curve rather than the power???????????????????????????????

2. Apr 7, 2010

### jack action

If you know the power and the rpm, then you know the torque of the engine (power = torque X rpm).

No engine goes to 0 rpm. You have to start at some base rpm, where slipping will occur (at the tires or at the clutch). If you assume the tires slip, you can use the lower "sliding" coefficient of friction until the speed of the engine corresponds with the one of the wheel.