Posted by Mariam on Sunday, January 12, 2014 at 1:14pm.
Problem 2 A 15 kg block is attached to a very light horizontal spring of force constant 400 N/m and is resting on a smooth horizontal table as shown in the figure below. Suddenly it is struck by a 3 kg stone traveling horizontally at 8 m/s to the right, whereupon the stone rebounds at 2 m/s horizontally to the left.
a) Find the speed of the 15 kg mass just after the collision.
b) Is the collision elastic?
c) Find the maximum distance that the block will compress the spring after the collision.

Physics  Damon, Sunday, January 12, 2014 at 2:24pm
Plus is right
original momentum = 3*8 = 24
so final momentum = 24
What does right after the collision mean I wonder. Nothing happens when it first hits the spring. I will look at the final outcome.
24 = 3(2) + 15 v
24 = 6 + 15 v
30 = 15 v
v = 2 m/s part a
Initially
(1/2) m v^2 = .5*3 * 64 = 96 Joules
Finally
.5*3*4 + .5*15*4 = 36 Joules
Not elastic part b
Oh my we lost some energy in that spring
I will say all that lost energy went into the spring, half on compression and half on expansion
(9636)/2 = 30 joules = .5 k x^2
.5 * 400* x^2 = 30
x = .387 m