A 15.0 kg box is pushed up an 8.00 m long frictionless incline inclined at an angle of 30.0 degrees above the horizontal in 4.2 seconds. Find the average power required.
The Attempt at a Solution
This isn't so much a homework problem it's an old exam problem that I can't for the life of me get. The answer key from my instructor says the answer is 140 W. I Have a weight a distance and a time, so I figure I can take my mass and gravity and get the total force, and then I should be able to take the distance time Cos(30) and multiply that by 147N to get the work put that over the time and that should be the average power. but it comes out to 198 and that's not right. Any help is greatly appreciated.