Physics Help AP Phyics B. PLease help by EXPLAINING?

Question

4. Two air track carts move toward one another on an air track. Cart 1 has a mass of .45kg and a speed of 1.1 m/s. Cart 2 has a mass of .65kg (a) what speed must cart 2 have if the total momentum of the system is to be zero.(b) since the momentum of the system is also zero, does it follow that the kinetic energy of the system is also zero? (c) verify your answer to pat (b) by calculating the system’s kinetic energy.
6. A 220- g ball falls vertically downward hitting the floor with a speed of 2.5 m/s and rebounding upward with a speed of 2 m/s. (a) find the magnitude of the change in the ball’s momentum (b) find the change in the magnitude of the ball’s momentum (c) which of the two quantities calculated in parts (a0 and (b) is more directly related to net force acting on the ball during the collision with the floor? explain?

Answer 1

4) Since the carts have motion in opposite directions

0.45*1.1-0.65*v=0
v=0.76 m/s

The energies are not zero
.5*0.45^2+.5*0.65*0.76^2
0.29 J

6)
starting momentum
-0.220*2.5
rebounding momentum
0.220*2

The magnitude of change is
0.22*4.5

Was b the change in kinetic energy?
Starting kinetic
.5*0.22*2.5^2
Rebounding kinetic
0.5*0.22*2^2

The magnitude of change is
0.5*0.22*(2.5^2-2^2)


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