Practice 6D: | 1 | 2
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Momentum and Impulse - by Stephanie Culnane,
2001
1.
A 63.0 kg astronaut is on a spacewalk when the tether line to the shuttle
breaks. The astronaut is able to
throw a 10.0 kg oxygen tank in a direction away from the shuttle with a speed of
12 m/s, propelling the astronaut back to the shuttle.
Assuming that the astronaut starts from rest, find the final speed of the
astronaut after throwing the tank.
Here's what you know,
astronaut's m = 63.0 kg, tanks = 10.0 kg, tank's v = 12.0 m/s. Use
the formula mv = mv. Plug in (10.0 kg)
(12 m/s) = (63.0 kg)(v).
astronaut's v = 1.9 m/s.
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2. An
85.0 kg fisherman jumps from a dock into a 135.0 kg rowboat at rest on the west
side of the dock. If the velocity of the fisherman is 4.30 m/s to the west as he
leaves the dock, what is the final velocity of the fisherman and the boat?
Here's
what you know, fisherman's m = 85.0 kg, boat's m = 135.0 kg, fisherman's v =
4.30 m/s. Use
the formula mv = mv.
Plug in (85.0 kg)(4.30 m/s) = (85.0 kg + 135.0 kg)(v).
v = 1.66 m/s.
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3. Each
croquet ball in a set has mass of 0.50 kg.
The green ball, traveling at 12.0 m/s, strikes the blue ball, which is at
rest. Assuming that the balls slide on a frictionless surface and
all collisions are head-on, fine the final speed of the blue ball in each of the
following situations:
a.
The green ball stops moving after it strikes the blue ball.
b. The green ball continues moving
after the collision at 2.4 m/s in the same direction.
c.
The green ball continues moving after the collision at 0.3 m/s in the
same direction.
Here's
what you know m = 0.50 kg, green ball's v = 12.0 m/s.
a. Use
the formula mv = mv.
Plug in (0.50 kg)(12.0 m/s) = (0.50 kg)(v).
v = 12.0 m/s.
b. Use
the formula mv = mv + mv.
Plug in (0.50 kg)(12.0 m/s) = (0.50 kg)(2.4 m/v) + (0.50 kg)(v).
v = 9.6 m/s.
c. Use
the formula mv = mv + mv.
Plug in (0.50 kg)(12.0 m/s) = (0.50 kg)(0.3 m/s) + (0.50 kg)(v).
v = 11.7 m/s
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4. A
boy on a 2.0 kg skateboard initially at rest tosses an 8.0 kg jug of water in
the forward direction. If the jug
has a speed of 3.0 m/s relative to the ground and the boy and skateboard move in
the opposite direction at 0.60 m/s, find the boy's mass.
The total momentum before and after is zero, so if the jug of water has a
momentum of (p = mv) (8.0 kg)(3.0 m/s) = 24 kgm/s forward, which means the
skateboard and boy must have gained an equal but opposite momentum backward.
So if p = mv, and p = 24 kgm/s backwards, and v = .60 m/s:
24 kgm/s = m(.60 m/s)
then the boy and his board must have a total mass of 40 kg, which means the boy
has a mass of 38 kg, if the board has a mass of 2 kg.
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