What is the average power delivered by the engine?

Question

A 1500-kg car accelerates from 0 to 25 m/s in 7.0 s. What is the average power delivered by the engine? (1 hp = 746 W)

Answer 1

Does Fred get your "A" for doing your entire homework set for you? You will not be able to cheat on the exam like this, and your evil plans will backfire.

Answer 2

Work done = force * distance = m*a*d and power = energy/time

The vo=0 and vf = 25 m/s and t=7 sec.  This gives...

3.6 m/s^2 as acceleration and d=87.5 meters and thus F=ma= 5400 N.

Energy = 5400*87.5 = 4.7E5 Joules (2 sig. figs) and Power = 67,500 Watts or 90 HP (2 sig. figs again).

-Fred

EDIT: Don't listen to jose (or his pussycats).  People learn in different ways.  It is helpful to have solutions when working these problems.  To see them...to unbderstand how to set them up and solve them.  You learn this way (Schaums outline series is all about this).  Obviously, if you don't learn the concepts behind the answers (or try some on your own) then you will not do well on tests in the future, but having a professor of physics and math "point you" in the right direction is a valuable way to learn physics.  I am providing you the net so that you don't fall academically speaking.  I am sure that jose says this because (s)he would just copy the work without thinking about it, but an education is what YOU make of it.

Good luck to you.  I am happy to answer future questions for you.

Thanks for the thumbs down, jojo.  Don't be ashamed if you don't understand the work.  Ask me, I'm happy to help you too!!  Not everyone is a natural scientist.

Answer 3

Fred...  

you've gone about the LONG way..

easier to find the car's kinetic energy..

E = (1/2)mv^2

and

Power = E/t

          

no need to find acceleration, and distance...