other helper already explains but here are two examples:
2. let N be +ve n S be -ve
N-going Zak momentum=mass*velocity=50*4=200
S-going Zak momentum=40*(-5)=-200
after collision, they get stuck together so their masses=50+40=90
by conservation of momentum:
200+(-200)=90*final vel
0=90*final vel
final vel=0m/s
3. cars have rear end collision so they were traveling in same direction be4
total momentum be4 collision=1200*20+1000*15=39000
cars continue 2 move as 1 mass after collision so final mass=1200+1000=2200
by conservation of momentum, final momentum=2200*final vel=39000
final vel=39000/2200=17.73m/s
plz post in comment if u need 4 n 5
4. Before the dog jumps out, initial momentum=0
After the dog jumps out, final momentum=initial momentum=0
So dog's momentum+canoe's momentum=0
Dog's momentum=mass*velocity
=15*1.2
=18
Canoe's momentum= -(dog's momentum)= -18
Canoe's velocity=-18/40=-0.45m/s
The - sign means the direction is opposity to the dog's jump.
5. Assume the Pennridge player's direction is +ve
Initial momentum before collision=Pennridge player's momentum + Souderton player's momentum
=80*3+70*(-2.5)
=240-175
=65
As they are stuck together after collision, the final mass=80+70=150
Final momentum=Initial momentum=65
Final velocity=Final momentum/Final Mass
=65/150
=0.4333m/s in Pennridge direction
