- #1

chubbyorphan

- 45

- 0

## Homework Statement

A kid on a sled slides down a hill from a rest position.

m=47.0kg

vertical displacement is 10.0m

## Homework Equations

a)For total mechanical energy I calculated (Egravity=mgh) to equal 46 x 10^2 J

b)*mentions we assume there is no friction or external pushes*

and for speed at the bottom of the hill I used (W = Ekf - Eki) to get 14m/s

I'm pretty confident these answers ^ are right but if someone wanted to double check them that'd be really cool, but what I'm really trying to check is what's next:

## The Attempt at a Solution

The final question asks..

'the child's actual speed at the bottom of the hill is 5.0m/s. explain whether or not this defies the conservation of energy'

my thoughts are yes.. because assuming there is no friction or external pushes.. for the speed at the bottom of the hill to be 5.0m/s we've lost energy we can't account for.

Can someone please tell me if I'm right?

also.. an example question in the book mentions 'a 55.0kg cyclist rides off the edge of a 5.0m high cliff with a speed of 15m/s'

.. then the sample answer says that 'the cyclist's gravitational potential energy is 2700 J and his kinetic energy is 6188 J'

does this mean that his total mechanical energy is the addition of these two figures? I'm thinking yes.. is that right?

Thanks in advance for any help!