Does Constant Engine Power Guarantee Constant Acceleration?

[jim_ringo]

Homework Statement

a cars engine produces constant power therefore the cars speed will increase at a constant acceleration.

is this true or false

Homework Equations

Power=w/t
work=fd
so P=mad/t

The Attempt at a Solution

so if p is constant it appears a must be constant. Therefore the statement is true

When I logically think about this situation I think it is false. I imagine myself driving down the highway in my stang turning 2500 rpm at 100 mph. Assume I stay in the same gear. Unless I raise the revs by giving it more gas I will not accelerate. When raising the engine rpm my engine makes more power...so how can I accelerate if my engine maintains a constant rpm(same power output)?

 

[BOYLANATOR]

Your equations are correct and so is your logic. However, can you think of any additional forces which may act against the acceleration of the car?

 

[jim_ringo]

Ah, wind resistance and friction between the road and tires...and then there's also the some power loss due to the weight of the drive train components.

 

[BOYLANATOR]

Yeah. I think it's funny to think about a bike. The wheels are so thin, but that little surface area combined with the air stops you from going as fast as you want.

 

[jim_ringo]

so just that little bit of resistance from the tires and the air hitting the body of the car prevents the car from accelerating,correct?

 

[jim_ringo]

so the answer would be true?

 

[BOYLANATOR]

Yes, so it's not that little really.

 

[BOYLANATOR]

so the answer would be true?

Well in real life the answer is false for a car. A rocket in deep space could accelerate indefinitely.

 

[NascentOxygen]

a cars engine produces constant power therefore the cars speed will increase at a constant acceleration.

is this true or false

Homework Equations

Power=w/t
work=fd
so P=mad/t

The Attempt at a Solution

so if p is constant it appears a must be constant. Therefore the statement is true

Whoa! I'm not convinced that you have demonstrated it to be true. All I see you having shown here is that
the factor (ad/t) is constant. I think you are asked to determine whether or not a is constant---am I correct in believing that is what the problem is asking?

 

[jim_ringo]

Whoa! I'm not convinced that you have demonstrated it to be true. All I see you having shown here is that
the factor (ad/t) is constant. I think you are asked to determine whether or not a is constant---am I correct in believing that is what the problem is asking?

Yes that is what the problem is asking