## Work and energy quiz

foodyogamedicine
Posts: 7
Joined: Tue Jan 29, 2019 9:21 pm

### Work and energy quiz

On slide 12 this question asks: a man pushes a 50 kg crate up a frictionless ramp with an inclined plane of 30 degrees and a length of 10m. How much work must be done to push the crate to the top?

The explanation says to use the work-energy theorem to calculate the change in potential energy as the work done to equal 2500 J. When I calculated it using Work = Fdcos(30) I got ~ 4300J what did I do wrong in my calculation??

Thank you!
NS_Tutor_Mathias
Posts: 616
Joined: Sat Mar 30, 2019 8:39 pm

### Re: Work and energy quiz

I'm going to guess it is the trigonometry that is tripping you up.

A 30/60/90 right triangle, such as the cross-section of a wedge-shaped ramp, has sides 1/root3/2. If the ramp is 10 meters long, therefore the height is half that: 5 meters.

(Or in mathematical notation (sin30)*10=5)

So we arrive at mgh = 50*10* 5 = 2500 J

Let me know if this helps, or if the hangup was elsewhere!