Iunderstand it, but i got confused on the part where it says that they move as one mass or get stuck together

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

the minimum amperage that the current in this wire would have to have so that its weight is completely supported by the magnetic force due to earth's field, assuming that no other forces except gravity act on it