AP Physics Whiteboards
Impulse & momentum
1. A neutron of mass 1.67 x 10–27 kg collides head-on with a deuterium nucleus at
rest. The deuterium has a mass of 3.34 x 10–27 kg. The speed of the neutron is
8.80 km/s before the collision and the collision is elastic.
a. What are the speeds of the deuterium nucleus and the neutron after the
collision?
b. What is the total kinetic energy?
2. A 0.11 kg baseball is thrown with a speed of 17 m/s towards a
batter. After the ball is struck by the bat, the ball has a speed of 34
m/s and a direction of 60° above the horizontal toward the infield.
If the ball and bat are in contact for 0.025 s, find the magnitude of
the average force exerted on the ball by the bat.
3. Two identical ball bearings collide head-on. The initial velocity of
one is 0.75 m/s, while that of the other is –0.43 m/s. If the collision is perfectly
elastic, what is the final velocity of each ball bearing?
4. A 20 g bullet moving horizontally at 50 m/s strikes a 7 kg block resting on a table.
The bullet is embedded in the block after the collision.
a. Find the speed of the block after the collision.
b. Find the frictional force between the table and the block if the block
moves 1.50 m before stopping.
c. What is the coefficient of kinetic friction between the block and the table?
5. A missile of mass M constructed by the lowest
bidder is moving with a velocity of 200 m/s and
explodes in midair, breaking into two parts of mass
M/4 and 3M/4. If the smaller piece flies off at an
angle of 60° with respect to the original direction of
motion, with an initial speed of 400 m/s, what is the
initial velocity of the other piece? You may ignore
the effect of gravity.
6. A 0.30 kg block slides down the side of a frictionless
hemispherical bowl with a radius of 0.10 m. At the
bottom it collides perfectly inelastically with a 0.40 kg
mass initially at rest.
a. What impulse is given to the 0.40 kg mass?
b. Find the maximum angle the radius vector to the
combined masses will make with the vertical (α)
after the collision.
ap_wb_04.docx -- froehlich
7. A uranium nucleus of initial mass 3.8 x 10–25 kg emits an alpha particle of mass
6.4 x 10–27 kg with a velocity of 1.0 x 107 m/s. What is the recoil velocity of the
resulting thorium nucleus?
8. The two balls shown in the figure below collide and bounce off each other.
a. What is the final velocity of the 500 g ball if the 800 g ball has a speed of
15 cm/s after the collision?
b. Is the collision perfectly elastic?
9. A wagon with two boxes of gold, having a total mass of 300 kg, is cut loose from
the horses by an outlaw when the wagon is at rest 50 m up a 6.0 degree slope. The
outlaw plans to have the wagon roll (without friction, of course) down the slope
and across the level ground, and then fall into a canyon, where his confederates
wait. In a tree 40 m from the canyon edge wait the Lone Ranger (75 kg) and
Tonto (60 kg). They drop vertically into the wagon as it passes under them.
a. If they require 5.0 s to grab the gold and jump out, will they make it before
the wagon goes over the edge?
b. When the two heroes drop into the wagon, is the kinetic energy of the
system of the heroes plus the wagon conserved? If not, does it increase or
decrease, and by how much?
10. In a shipping company distribution center, an open cart of
mass 50.0 kg is rolling to the left at a speed of 5.00 m/s.
You can ignore friction between the cart and the floor. A
15.0 kg package slides down a chute that is inclined at 37°
from the horizontal and leaves the end of the chute with a
speed of 3.00 m/s. The package lands in the cart and they
roll off together. The lower end of the chute is a vertical
distance of 4.00 m above the bottom of the cart.
a. What is the speed of the package just before it
lands in the cart?
b. What is the final speed of the cart?
ap_wb_04.docx -- froehlich