Hi, I'm just doing my Applied Maths h/worl at the mo which is pretty much just mechnics and I was hoping someone here could give me a hand. I think my problem here is more a case of my brain shutting down early for rimbo as opposed to the h/work being difficult so here I go.......(adsbygoogle = window.adsbygoogle || []).push({});

The first problem I'm having is this one-

One end of an elestic string of natura; length l and modulus lambda is fixed to a point O on a rough horizontal table (its 'spring constant' is k/lambda). The other end is attached to a particle P of mass m. The system is released from rest with P lying on the table and the distance OP being 2l. If lambda=3mg and u (coefficient of friction)=1 between the table and the particle, show that-

a) the dtring eventually becomes slack

b)the particle comes to rest at a distance l/2 from O.

For part a Ive been using the work energy theorum because if at B (a distance l from O, as in at the natural length), the velocity is greater than 0 then the particle will keep on moving so the string will become slack. so I'm using KE+PE at P minus KE+PE at B= work done my the frictional force. So at P we'd only have PE since it's at rest and is it true that at B we'd only have KE since the particle would be at the string's natural lenth therefore the string wouldn't be strectched in anyway? I've got work done by the frictional force as -mgl which I'm assuming is ok. My problem is hat Im end up with my velocity at B to be the square root of 5gl, which I have a feeling is wrong because for part b I'm not getting the ansewet to be l/2. For part b I'm using rhe fact that there's no tension so only friction acts to slow the particle down so I'm using the eqt of motion v^2=u^2+2as, but I'm getting 5l/2 out of this. Can anyone shed any lioght on this for me?

The next one is just short. If we have a ski-jump slope and the jumper goes off the bottom of it moving horitzonally, how do you work out the verticla components? I've got u=0, a=g and s=-h (of h is the hgith above the ground when taking off). However if you put that into an ewqt of motion you end up with a complex number so what is going wrong?

Claire

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Some quick h/work help please!

**Physics Forums | Science Articles, Homework Help, Discussion**