# Homework Help: Need help. Momentum. Lost!

1. Oct 29, 2008

### grizzy225

Need help for Final Physics Exam. Gen Physics 1?
I was given a bunch of problems from out of my book. I've cruised through most but chapter 8 is giving me a real hard time. Here are some examples from the chapter, any help with these type problems would be great.

1. Block A has mass 1.00kg, and block B has mass 3.00kg. The blocks are forced together, compressing a spring S between them; then the system is released from rest on a level frictionless surface. The spring, which has a negligible mass, is not fastened to either block and drops to the surface after it has expanded. Block B acquires a speed of 1.20 m/s. (a) What is the final speed of block A? (b) How much potential energy was stored in the compressed spring?

2. A 15.0 kg block is attached to a very light horizontal spring of force constant 500.0 N/m and is resting on a frictionless horizontal table. Suddenly it is struck by a 3.00kg stone traveling horizontally at 8.00 m/s to the right, whereupon the stone rebounds at 2.00 m/s horizontally to the left. Find the maximum distance that the block will compress the spring after the collision.

3. A rifle bullet with mass 8.00g strikes and embeds itself in a block with a mass of 0.992kg that rests on a frictionless, horizontal surface and is attached to a coil spring. The impact compresses the spring 15.0cm. Calibration of the spring shows that a force of 0.750 N is required to compress the spring 0.250 cm. (a) Find the magnitude of the block's velocity just after impact. (b) What was the initial speed of the bullet?

2. Oct 29, 2008

### Stovebolt

What have you tried on these problems up to this point?

One thing I can help you with is to point out that momentum will be conserved in each problem - whatever you start with will be equal to what you finish with since there are no sources of loss (e.g., friction).