Initial acceleration

jeudi 31 octobre 2013

1. The problem statement, all variables and given/known data

I need to find the initial acceleration of a steel object that weighs .89 kg, that is pulled along a steel a rail by a cord. The cord is at an 45 degree angle and has a tension of 21 N. The friction coefficents(spelled right?) of steel on steel are: .8 for static friction, .6 for kinetic friction and .002 for for rolling friction.

2. Relevant equations

F=ma

Fp=21 N

3. The attempt at a solution

What i did was seperate the net forces into the x direction and the y direction. In the x direction i got Fpcos(theta)-Fk=max (x = x direction). I then solved for ax giving me (Fpcos(theta)-Fk)/m.

Since Fk =ukFn (kinetic friction coefficent * normal force), i substituted that in for Fk in ax. In the y direction i got, Fpsin(theta)+Fn-Fe=0. I solved for Fn then substituted that back in for Fn in the ax equation getting: (Fpcos(theta)-uk(Fe-Fpsin(theta)))/m. No sig figs required, since the problem doesnt say anything about it