# Calculating the energy in a part of a rollercoaster

1. Sep 27, 2015

### lamefeed

Hi(This thread might have been posted in the wrong section of the forum although this isn't a homework problem, just something I do because I like physics!), I've been trying to figure out how to solve this problem for a few hours, but whatever I do it seems to give me the wrong answer.

h(1)= 50m
v= 0.5 m/s

$E = E_k + E_p$
Which gives me this formula
$E = \frac{1}{2}mv^2 + mgh$
After this I remove the mass since it's not been given in the task, and i'm left with:
$E = \frac{1}{2}v^2+ gh$
When I fill in the numbers I get this:
$E = \frac{1}{2}0.5^2 + 9.81*50 = 490 J$

But I'm supposed to get 49 J ?!

Can't get any help from my teacher until tomorrow so would be lovely if some of you could tell me where I took a wrong turn(If I made a mistake)!

Cheers,
Lamefeed

Last edited: Sep 27, 2015
2. Sep 27, 2015

### Staff: Mentor

Something is wrong with the problem statement, because you need the mass. A grain of sand at the top of a 50 meter ramp represents a lot less potential energy than a brick at the top of the same ramp. You answer would be right if the cart had a mass of 1 kg, the book would be right if it had a mass of .1 kg, and yes, if you want more help with this problem you should start a thread in the homework section.

This thread is closed; OP will restart in the HW section if necessary.