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Practice problems for Energy Unit:
Use the equations below to answer the following questions. Show all of your work as if
this was a test and each question was worth 4pts.
Equations:
Momentum= (mass) ( velocity) =  = mv
Impulse = (Force) (time) = Change in momentum = Ft = mv
Work = (Force) (distance) = W = Fd
Power =Work  time = P = W/t
PE = mgh
KE = 1/2 mv2
1. What is the momentum of a 1kg ball that is rolling 20m/s?
2. Cameron is snow boarding out of control and runs into a tree. He was going
11m/s and has a mass of 100kg. His collision with the tree took 0.5 sec. With
how much force did Cameron hit the tree?
3. A ball is moving at 4m/s and has a momentum of 48 kg-m/s. What is the ball’s
mass?
4. A 30 kg girl and a 25 kg boy face each other on friction-free roller blades. The
girl pushes the boy, who moves away at a speed of 1m/s. The girl’s speed is now
_______________________. (Use the Law of Conservation of Momentum)
5.
A.) How much potential energy does a 80 kg high diver have while standing on
top of a 25 m platform?
B.) The diver jumps off the platform. How much kinetic energy does the same
diver have before he hits the water?
C.) What Law did you use to answer the question above?
D.) What is the velocity of the diver when he hits the water?
6. A.) How much work is needed to lift a 100N block 4m?
B.) How much work is needed to drag the block up a ramp if the top of the ramp
is 4 m off the ground and I neglect friction?
C.) What is the force needed to push the block up the ramp if the ramp is 9m
long?
D.) How much power does the person have if they accomplish this work in 3s?
7. It takes 300J of energy to move a ball 3m. How many Newtons does the ball
weigh?
Practice problems for Energy Unit:
1. p = mv m = 1 kg v = 20 m/s
KEY
p = (1 kg) (20 m/s) = 20 kg m/s = 2 X 101 kg m/s
F= mv = m(v2 – v1)
t
t
3
F = (100kg) (0 m/s -11 m/s) = -1100 kg m/s = - 2.2 x 10 N
(0.5 s)
(0.5 s)
3. p = mv
m = p / v p = 48 kg m/s v = 4 m/s
2. Ft=mv
4.
m= 100 kg v = 11 m/s
t = 0.5 s F = ?
48 kg m/s) = kg = 1.2 x 101 kg
(4 m/s)
m v (initial) = m v (final) m v (girl) = m v (boy)
( 30kg)( v (girl) ) = (25 kg) (1 m/s) =
m (girl) = 30 kg
m (boy) = 25 kg
v (girl) = ?
v (boy) = 1 m/s
8.3 x 10-1 kg
5.
A. PE = mgh m = 80 kg g = 9.8 m/s2 h = 25 m
PE = (80 kg) (9.8 m/s2) (25 m) = 19600 joules = 1.96 x 104 J
B.
6.