Physics Homework- Need help. Inelastic Collision Problem?

Question

A 15.0 kg object moving in the +x direction at 5.5 m/s collides head-on with a 10.0 kg object moving in the -x direction at 4.0 m/s. Find the final velocity of each mass if:(a) the objects stick together, (b) the collision is elastic, (c) the 15.0 kg oject is at rest after the collision, (e) the 15.0 kg object has a velocity of 4.0 m/s in the -x direction after the collision.

I have the answers, but I dont understand how they were derived: (a) 1.7 m/s for both (b) -2.1 m/s, 7.4 m/s (c) 0, 4.3 m/s (d) 2.8 m/s, 0 (e) -4.0 m/s, 10.3 m/s

It doesn't matter if you can't get all of them. EVERY little bit helps.

Answer 1

(a) Initial momemtum = final momentum

Inelastic collision so they stick together (that is, have the same speed after the collision).

(15.0 kg) (5.5 m/s) + (10.0 kg) ( -4.0 m/s) = (25.0 kg) v

Solve for v.

(b) In elastic collisions, kinetic energy is also conserved.
Let v1 and v2 be the final velocities of the balls.

Conservation of momentum:

(15.0 kg) (5.5 m/s) + (10.0 kg) ( -4.0 m/s) = (1.50 kg) v1 + (10.0 kg) v2

Conservation of kinetic energy:

1/2 (15.0 kg) (5.5 m/s)^2 + 1/2 (10.0 kg) ( -4.0 m/s)^2 = 1/2 (1.50 kg) v1 ^2 + 1/2 (10.0 kg) v2^2

You have two linear equations and two unknowns (v1 and v2). Solve them using whatever technique you have been taught to solve systems of linear equations.

(c) Partially elastic collision so only momentum is conserved.

(15.0 kg) (5.5 m/s) + (10.0 kg) ( -4.0 m/s) = (1.50 kg) (0) + (10.0 kg) v2

Solve for v2.

(d) Again, only momentum is conserved

(15.0 kg) (5.5 m/s) + (10.0 kg) ( -4.0 m/s) = (1.50 kg) (4.0 m/s) + (10.0 kg) v2

Solve for v2.

Answer 2

Kinetic skill of the bullet a million/2 m * v**2 is comparable to the flair skill of the mixed mass of the bullet and block= (m+3m)*g*h. Equate those parts and sparkling up for h. g is the acceleration by using gravity. So the best answer is h=v**2/8g by using fact that there is in basic terms one unknown (h), in basic terms one equation: conservation of skill is important. the different answer has an further 4 interior the KE term otherwise he/she might are starting to be the comparable answer yet with better unneeded artwork. The KE is in basic terms for the bullet mass, if the two hundreds after impression are used the speed may be smaller.