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Ch 7 Practice Problems
∆p = m∆v
∆v=(vf - vo)
J=F∆t
F∆t = m∆v
m1ov 1o + m2ov 2o = m1f v 1f + m2fv 2f
m1ov 1o + m2ov 2o = (m1 + m2 ) vf
(m1 + m2 ) vo =
m1fv 1f + m2fv 2f
1. a. What is the momentum of an 8kg bowling ball rolling at 2 m/ s?
b. if the bowling ball rolls into a pillow and stops in .5 s, calculate the average force it exerts
on the pillow.
c. What average force does the pillow exert on the ball?
∆p = m∆v
∆v=(vf - vo)
J=F∆t
F∆t = m∆v
m1ov 1o + m2ov 2o = m1f v 1f + m2fv 2f
m1ov 1o + m2ov 2o = (m1 + m2 ) vf
(m1 + m2 ) vo =
m1fv 1f + m2fv 2f
2. a. What is the momentum of a 50 kg carton that slides at 4 m/ s across an icy surface?
b. The sliding carton skids onto a rough surface and stops in 3 s. What is the change in
momentum of the carton?
c. What was the impulse that changed the momentum of the carton, thus bringing it to a stop
d. Calculate the force of friction the carton encountered in order to stop it in 3 s.
∆p = m∆v
∆v=(vf - vo)
J=F∆t
F∆t = m∆v
m1ov 1o + m2ov 2o = m1f v 1f + m2fv 2f
m1ov 1o + m2ov 2o = (m1 + m2 ) vf
(m1 + m2 ) vo =
m1fv 1f + m2fv 2f
3. a. What impulse occurs when an average force of 10 N is exerted on a cart for 2.5 s?
b. What change in momentum does the cart undergo?
c. If the mass of the cart is 2 kg and the cart is initially at rest, calculate its final speed.
∆p = m∆v
∆v=(vf - vo)
J=F∆t
F∆t = m∆v
m1ov 1o + m2ov 2o = m1f v 1f + m2fv 2f
m1ov 1o + m2ov 2o = (m1 + m2 ) vf
(m1 + m2 ) vo =
m1fv 1f + m2fv 2f
4. A 2 kg blob of putty moving at 3 m/ s slams into a 2 kg blob of putty at rest.
Calculate the velocity of the two stuck-together blobs of putty immediately after colliding.
∆p = m∆v
∆v=(vf - vo)
J=F∆t
F∆t = m∆v
m1ov 1o + m2ov 2o = m1f v 1f + m2fv 2f
m1ov 1o + m2ov 2o = (m1 + m2 ) vf
(m1 + m2 ) vo =
m1fv 1f + m2fv 2f
5. Dom is at Busch Gardens playing the arcade games. At one booth, he is throwing
baseballs at stacked bottles trying to knock them over. He has one ball & one bottle left
standing. He throws a .5 kg ball forward with a velocity of 21 m/ s and hits the 0.2 kg bottle.
When the ball hits the bottle, the bottle moves forward with a velocity of 30 m/ s and falls
off of the table. What is the velocity of the ball after it hits the bottle?
∆p = m∆v
∆v=(vf - vo)
J=F∆t
F∆t = m∆v
m1ov 1o + m2ov 2o = m1f v 1f + m2fv 2f
m1ov 1o + m2ov 2o = (m1 + m2 ) vf
(m1 + m2 ) vo =
m1fv 1f + m2fv 2f
6. Hayden rolls a 7 kg bowling ball down the alley trying to get a spare. One pin is still
standing, and Hayden’s bowling ball hits the pin head-on with a velocity of 9 m/ s. The 2 kg
pin acquires a forward velocity of 14 m/ s. What is the new velocity of the bowling ball?
7. A 620 kg moose stands in the middle of the railroad tracks, frozen by the lights of an oncoming 10,000 kg locomotive that is traveling at 10 m/ s. The engineer sees the moose but
is unable to stop the train in time and the moose rides down the track sitting on the
cowcatcher in the front of the locomotive (uninjured of course). What is the new combined
velocity of the locomotive and the moose?
∆p = m∆v
∆v=(vf - vo)
J=F∆t
F∆t = m∆v
m1ov 1o + m2ov 2o = m1f v 1f + m2fv 2f
m1ov 1o + m2ov 2o = (m1 + m2 ) vf
(m1 + m2 ) vo =
m1fv 1f + m2fv 2f
8. Miles is sitting on a skateboard at rest. The combined mass of Miles and the skateboard
is 60 kg. John throws a 10 kg medicine ball at Miles with a velocity of 3 m/ s. Miles catches
the medicine ball which causes Miles and the skateboard to move. What will be the velocity
of Miles & the medicine ball on the moving skateboard?