Momentum and energy two sled questions for physics

[skuller]

momentum and energy two sled questions for physics...

I have tried to solve these questions but sleds to me are just very confusing and hard...I really need help with this.

A sled starts from rest at the top of the frictionless, hemispherical, snow-covered hill shown in the figure.

a) Find an expression for the sled's speed when it is at angle theta.

b) Use Newton's laws to find the maximum speed the sled can have at angle theta without leaving the surface.

c) At what angle theta_max does the sled "fly off" the hill?


I have the picture of this problem right here...

http://img703.imageshack.us/img703/7765/sled.png









A new event has been proposed for the Winter Olympics. An athlete will sprint 100 m, starting from rest, then leap onto a 20 kg bobsled. The person and bobsled will then slide down a 50-m-long ice-covered ramp, sloped at 20 degrees , and into a spring with a carefully calibrated spring constant of 2000 N/m. The athlete who compresses the spring the farthest wins the gold medal. Lisa, whose mass is 40 kg, has been training for this event. She can reach a maximum speed of 12 m/s in the 100 m dash.

here is a diagram of this i uploaded...


http://img521.imageshack.us/img521/7765/sled.png



I know for one of them I need the centripetal acceleration and for the other I need mv for momentum and spring potential energy then I am clueless

 

[Mindscrape]

Hello skuller, welcome to the forums. Don't feel bad, these are very tough questions. We generally require that you show some of your attempt before we help you out. We can't help you to gain more knowledge when we don't even know where your starting level is.

Try something out, even if you get it wrong the act of you trying will be helpful to you. If you can do the whole problem, but you get it wrong that's fine. If you do a tiny bit of the problem right, then get stuck, that's fine too.

 

[Mindscrape]

Here, I'll give you a kick-start since I see you haven't responded and must still be struggling. If you use conservation of energy you can get the velocity at any position on the semi-circle. The trick after that is to come up with the balance of forces that will tell you when the sled is about to leave the track.

 

[Mindscrape]

The second question is a bit easier and you should be able to get it through many possible methods, though once again, conservation of energy will make life easier on you.