Work and energy without friction

[catmd13]

Homework Statement

A physics student shoves a 0.50-kg block from the bottom of a frictionless 30.0° inclined plane. The student performs 4.0 J of work and the block slides a distance s along the incline before it stops. Determine the value of s in cm.

Homework Equations

W=(Fcostheta)s

The Attempt at a Solution

In the problem we have the weight of the block the degree of the incline and the work done. i was wondering how I would find F cause wouldn't W=4.0J cos=30.0.

 

[mgb_phys]

The energy only depends on the vertical distance traveled.
Find that from W=mgh and then simple trig gives you the distance along the slope

 

[Doc Al]

Don't worry about trying to figure out the force that the student exerted (assuming that's what you mean by F). You don't have enough information and it's not needed anyway.

Hint: Use conservation of energy.

 

[catmd13]

I did W=mgh
4.0J=(0.50kg)(9.80)h

Im still getting the wrong answer am i using the wrong equation or an error in my math

 

[Doc Al]

I did W=mgh
4.0J=(0.50kg)(9.80)h

Im still getting the wrong answer am i using the wrong equation or an error in my math

That equation will give you the height, which is the first step. Now use a bit of trig (as mgb_phys said) to find the distance along the incline that corresponds to that height.

 

[catmd13]

i get 180 cm is this correct

 

[Doc Al]

i get 180 cm is this correct

No. Show the steps you used to get that result.