# Way to find acceleration if I know the kinetic energy

Is there any way to find acceleration ( horizontally ) if I know the kinetic energy, mass and velocity of an object?

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Delphi51
Homework Helper

No. Acceleration causes energy and velocity to change. You would need to know something about the change in energy or velocity to work back to the acceleration.

OK, if I know the force of friction and so its acceleration and the velocity of the moving object, can I work out the time for it to stop by t= forward velocity/acceleration of friction? So that velocity will slow down at a constant rate for which the acceleration of friction says?

Delphi51
Homework Helper

Yes.

No that can't be right as then I get the acceleration due to friction as the same as the acceleration forwards. If that is true then F = MA is the same forward and backwards ( as the mass is the same ). That would mean it does not accelerate at all, which I know is not true. Back to the drawing board :)

Delphi51
Homework Helper

Say you have a car moving in the positive direction at 10 m/s on a level road, engine not running. Mass 1000 kg, force of friction -500 N.
The acceleration due to friction is F = ma, a = F/m = -500/1000 = -0.5 m/s².
Using a = Δv/Δt, Δt = Δv/a = (0-10)/-0.5 = 20 seconds
is the time to stop.

acceleration due to friction as the same as the acceleration forwards
In my little example, there is no acceleration forwards.
If there is acceleration forward, there must be a net force F = ma on the object and that net force is the forward force minus the friction force.

OK, that is what I have done so far. Yes, there is no acceleration forwards ;) I have been just trying anything without thinking :) So, I can never know the force that is pushing it with the info I have? I don't need it to answer any questions I was just trying to work it out.

So, in your car example are there only three forces? Friction, Weight and normal reaction force?

Delphi51
Homework Helper

Yes. The car pushes down on the road and the road pushes back up on the car with an equal force. So friction is the net force, equal to ma.
That is the only force pushing the car.

Is there any way to find acceleration ( horizontally ) if I know the kinetic energy, mass and velocity of an object?

According to your initial statement of the question, the answer is no.
KE = 1/2 mv^2, so you have the KE from the m and v anyway. There's nothing about acceleration there. Are the assumptions of gravity and friction warranted?

no you can not more information must be given to do so.