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**1. Homework Statement**

A bullet with a mass of 7.00 , traveling horizontally with a speed of 400 , is fired into a wooden block with mass of 0.850 , initially at rest on a level surface. The bullet passes through the block and emerges with its speed reduced to 200 . The block slides a distance of 48.0 along the surface from its initial position.

What is the coefficient of kinetic friction between block and surface?

What is the kinetic energy of the block at the instant after the bullet passes through it?

**2. Homework Equations**

P=m1v1 + m2v2

KE = 1/2mv^2

...I think, I'm not completely sure on if it is elastic or inelastic. Our physics book is honestly terrible and has no examples relating to this.

**3. The Attempt at a Solution**

I really have no idea where to start. I've tried setting the momentums equal to eachother and solving for v, but that doesn't work.

Second question:

A blue puck with a mass of 3.80×10−2 , sliding with a speed of 0.200 on a frictionless, horizontal air table, makes a perfectly elastic, head-on collision with a red puck with mass , initially at rest. After the collision, the velocity of the blue puck is 2.0×10−2 in the same direction as its initial velocity.

Find the magnitude of the velocity of the red puck after the collision.

Find the mass of the red puck.

Once again, no idea where to start.