Download HW11 - University of St. Thomas

Physics 111 HW11
Due Monday, 20 June 2016
CP01. An open-topped freight car with mass 24,000 kg is coasting without friction along
a level track. It is raining very hard, and the rain is falling vertically downward.
Originally, the car is empty and moving with a speed of 4.00 m/s. What is the speed
of the car after it has collected 3000 kg of rainwater?
CP03. Ice-hockey star Wayne Gretzky is skating at 13.0 m/s toward a defender, who in
turn is skating at 5.00 m/s toward Gretzky. Gretzky’s weight is 756 N; that of the
defender is 900 N. Immediately after the collision, Gretzky is moving at 1.50 m/s in
his original direction. You can ignore external horizontal forces applied by the ice to
the skaters during the collision.
a) What is the velocity of the defender immediately after the collision?
b) Calculate the change in the combined kinetic energy of the two players.
CP05. Two ice skaters, Daniel (mass 65.0 kg) and Rebecca (mass 45.0 kg), are
practicing. Daniel stops to tie his shoelace and, while at rest, is struck by Rebecca, who
is moving at 13.0 m/s before she collides with him. After the collision, Rebecca has a
velocity of magnitude 8.00 m/s at an angle of 53.1o from her initial direction. Both
skaters move on the frictionless, horizontal surface of the rink.
a) What are the magnitude and direction of Daniel’s velocity after the collision?
b) What is the change in total kinetic energy of the two skaters as a result of the
collision?
CP07. At the intersection of Texas Avenue and University
Drive, a blue, subcompact car with mass 950 kg traveling east
on University collides with a maroon pickup truck with mass
1900 kg that is traveling north on Texas and ran a red light
(see figure). The two vehicles stick together as a result of the
collision and, after the collision, the wreckage is sliding at
16.0 m/s in the direction 24.0o east of north. Calculate the
speed of each vehicle before the collision. The collision
occurs during a heavy rainstorm; you can ignore friction
forces between the vehicles and the wet road.
J01. A spring pushes a 2kg mass on a level frictionless table. The mass starts at rest and
when it leaves the spring 5 seconds later it is going 3 m/s.
a) Find the impulse delivered to the mass.
b) Find the average force on the mass during the time it pushes the mass.
J02. A baseball has a mass 0.145 kg.
a) If the velocity of a pitched ball has a magnitude of 45.0 m/s and the batted ball’s
velocity is 55.0 m/s in the opposite direction, find the magnitude of the change in
momentum of the ball (the impulse) applied to it by the bat.
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b) If the ball remains in contact with the bat for 2.00 ms, find the magnitude of the
average force applied by the bat.
J05. A soldier on the firing range fires burst from a .50 M2 Browning machine gun at a
full automatic rate of 20 rounds per second. Each bullet has a mass of 160 g and a
speed of 900 m/s relative to the ground as it leaves the barrel of the weapon. Calculate
the average recoil force exerted on the weapon during that burst.
J07. A soccer ball goes east at 5 m/s when it is kicked by a soccer player. After the kick,
it is going NW at 15 m/s. If the ball is in contact with the player’s foot for 0.08 seconds,
calculate the average force (magnitude and direction) the player delivers to the ball
during the kick.
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