Equations..?

Question

I have a physcis test tommarow andI was wondering about some equations.
I know momentum is= p=mv

Here is an Example
4. Running at 2.0m/s, Bruce, the 45kg quarterback, collides with Biff, the 90kg tackle, who is traveling at 7.0m/s in the other direction.
c. Calculate the total initial momentum of the system.
d. Upon collision, Biff continues to travel forward at 1.0m/s. Calculate his new momentum.
e. Using conservation of momentum, calculate Bruce's new momentum. In which direction is he moving?
f. Calculate Bruce's new velocity.


Can someone explain how you do these problems. Please.

Answer 1

c. Total initial momentum is Biff's momentum - Bruce's momentum, since they are in opposite directions.
p = p1 - p2
p = (7 m/s * 90 kg) - (2 m/s * 45 kg)
p = 630 - 90
p = 540 Nm

d. New momentum = mass * new velocity
p = mv
p = 90 kg * 1 m/s
p = 90 Nm

e. Bruce's momentum = total momentum - Biff's new momentum (since they're all in the same direction now)
p2 = p - p1
p2 = 540 Nm - 90 Nm
p2 = 450 Nm

f. New velocity = new momentum / new mass
p = mv, so v = p/m
v = 450 Nm / 45 kg
v = 10 m/s