Unit 1/2 Physics help? (Momentum/Impulse)

[Andiio]

Discuss the accuracy of the following. Make estimates of the physical characteristics of the colliding objects so that you can support your arguments with calculations.

a) When you bounce a basketball onto the ground, there is a collision between the Earth and the basketball. The total momentum of the system of the Earth and the basketball is conserved. Therefore, the Earth moves as a result of the collision.

b) When a car collides with a solid concrete wall firmly embedded into the ground, the total momentum of the system is conserved. Therefore, the concrete wall moves, but not quickly or far enough to allow any measurement of the movement to be made.

(I wrote for a): A basketball's mass, when compared with that of the Earth, is miniscule. Thus when a basketball and the Earth collide, the Earth will not move from the collision.) <- Is that right?

Thanks in advance!

[appianway]

a) Say that the mass of the earth (M) is much larger than the mass of the ball (m). Thus MV = -mv, and V= -mv/M... which is exceptionally small. So it moves, but the velocity is tiny.

b) If the concrete is FIRMLY embedded in the ground, it's part of the earth and hence momentum is transferred to the earth. Hence you can't really make a measurement as your reference frame is moving.

[Andiio]

Thanks appianway!!!