# Help on a dynamics/kinematics problem.

1. Jan 22, 2012

### Abdilatif

1. The problem statement, all variables and given/known data
http://myclass.peelschools.org/sec/11/22607/Lessons/Unit 2 Dynamics/Review Chapter 2.pdf Question 12, a and b?

2. Relevant equations
F=ma , Force = mass* acceleration
a=g(m2-usm2)/(m1+m2), g=gravity, us=coefficient of static friction, m1=mass1, m2=mass2

3. The attempt at a solution
a=F/m so the mass would be 6Kg, if i use the mass of the whole system. The force, would be only for the mass being acted on, which is F=mg, so it is F=2*9.8=19.6N. That is the force acting on the system. So back to the first equation, F=ma, 19.6=6a, simple math and a=3.3m/s. The book has the same answer.

Though I am puzzled to why they use T=ma instead of using F=ma, what does T stand for? Also by doing some more math, you know that the general equation for a = g(m2-usm2) / m1+m2, g=gravity, us=coefficient of static friction. So, then when I plug in my values I get a negative value is that right? Either way, in which cases are acceleration negative, when accelerating backwards, or when falling?

2. Nov 11, 2012