Help!!!!!!!!!!!! a couple physics questions.. (easy)?

here are some physics questions... any answers are helpful!! THANKS IN ADVANCE :)

1. Imagine that you are hovering next to the space shuttle in an Earth orbit. Your buddy of equal mass, who is moving at 3 km/h with respect to the shuttle, bumps into you. If he holds onto you, how fast do you both move with respect to the ship?
__km/hr

2. A railroad diesel engine weighs four times as much as a freight car. If the diesel engine coasts at 11 km/h into a freight car that is at rest, how fast do the two coast after they couple?
___km/hr

3. Comic-strip hero Superman meets an asteroid in outer space and hurls it at 70 m/s. The asteroid is a hundred times more massive than Superman is. In the strip, Superman is seen at rest after the throw. Taking physics into account, what would be his recoil speed?
__ m/s
What is this in miles per hour?
__mph

possible equations:
p=mv (p=momentum, m=mass, v=velocity)
Pbefore=Pafter (after collision)
J=Ft (J=impulse, F=force, t+time)

THANKS!!! numbers 1 and 2 have been answered... and are correct!!! any help with 3????????

1. Momentum Before = Momentum After
m(3 km/h) + m(0) = (m + m)(V)
3km/h(m) = 2m(V)
3km/h = 2(V)
V = (3km/h)/2
V = 1.5 km/hr ANS

2. Momentum Before = Momentum After
(4M)(11km/h) + M(0) = (4M + M)V
4M(11 km/h) = 5M(V)
44 km/h = 5(V)
V = (44 km/h)/5
V = 8.8 km/h ANS

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1.
Suppose your mass = friends mass = m

speed of friend = v = 3m/s

Friend's momentum relative to the shuttle= m*3

Your momentum relative to the shuttle= m*zero = zero

Total initial momentum =m*3

After friend bumps into you and holds on to you combined mass = m+m = 2m

suppose you both move together with velocity V,

Final momentum = 2mV

But momentum is conserved,

Final momentum = Initial momentum

2mV =m*3

V =1.5 m/s=5.4 km/hr

You both move with speed 5.4 km/hr with respect to the ship
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2 A railroad diesel engine weighs four times as much as a freight car.
Suppose mass of freight car = m

Mass of engine = 4m

Initial momentum of engine =4m*11=44m kgkm/hr

Initial momentum of freight car = m*zero =zero

Final momentum =(4m+m) V

But momentum is conserved,

Final momentum = Initial momentum

5mV = 44m

V =44/5 km/hr= 8.8 km/hr

The two move with speed 8.8 km/hr after they couple
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3.
Mass of Superman = m

Mass of asteroid =100*mass of Superman .

Mass of asteroid =100m

Superman meets an asteroid in outer space and hurls it at 70 m/s

momentum of superman = 70 m

momentum of asteroid =100m*V = momentum of superman = 70 m

V =70/100 = 0.7 meter/second

V =1.5658 miles per hour
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