- #1
PhysicsPhil
- 10
- 0
Homework Statement
A 1 kg object is moving along at speed of 5 m/s right before colliding with a 4 kg stationary object, in a perfectly inelastic collision.
Suppose that the objects are moving on a surface that has a coefficient of friction of mu=0.2. (Note you may still assume that the first object moves at 5 m/s immediately before collision. After impact, the objects move off in the velocity you calculated (which is 1m/s) and are then decelerated by friction until they come to a full stop
Homework Equations
I'm trying to understand how I can apply Newton's 2nd Law to this. We can solve this by using one of the Kinematics Equations, but we need to calculate acceleration. We know that Vi = 1m/s and that Vf = 0m/s (comes to a stop). But how can we calculate acceleration? I know it has to do with how to calculate the Force of Friction which is equal to mu*N (N is the normal force which is equal to -mg)
The Attempt at a Solution
So here is what the steps of the equation look like
(1) Calculate acceleration
(2) use Vf , Vi, and a to find t through the equation Vf = Vi + at
Then the solution has this
ma = F of friction = mu*m*g
therefore a = mu*g
(mu is Greek Letter meaning coefficient of friction)...
But how is this possible? I tried to think of it in terms of Fnet , but F-net :
Fnet = ma + mu*m*g (Find a from Newton's Second law[i/]
I don't see how "Find a from Newton's Second Law" works here...
But to do what the solutions did we would have to make Fnet = 0 ...
I don't see why we can do this? Is it because we are solving for the distance when it comes to a stop (which is 0 net force?)