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Physics A
Chapter 6 - Momentum and Impulse Practice Problems
1) If a blue whale has a mass of 1.46 × 105 kg and momentum of 9.73 × 105 kg•m/s to the south, what is its
velocity?
2) The current holder of the men’s world record for running 200 m is Michael Johnson, who in 1996 ran
200 m in 19.32 s. Johnson’s mass at the time of his record-breaking run was about 77 kg. What was the
magnitude of his momentum at his average speed?
3) The World Solar Challenge in 1987 was the first car race in which all the vehicles were solar powered. The
winner was the GM Sunraycer, which had a mass of 177.4 kg, not counting the driver’s mass. Assume that the
driver had a mass of 61.5 kg, so that the total momentum of the car and driver had a magnitude of
4416 kg•m/s. What was the car’s speed in m/s?
4) The brightest, hottest, and most massive stars (over 10 times as massive as the sun) are the brilliant blue stars
designated as spectral class O. If a class O star moves with a speed of 255 km/s and has a momentum of
8.62 × 1036 kg•m/s, what is the star’s mass?
5) A net force of 10.0 N to the right pushes a 4.0 kg book across a table. If the force acts on the book for 5.0 s,
what is the book’s final velocity? Assume the book to be initially at rest.
6) A billiard ball with a mass of 0.195 kg and a velocity of 0.850 m/s to the right is deflected by the cushioned
edge of the billiard table. The cushion exerts a force of 3.50 N to the left for 0.0750 s. What is the ball’s final
velocity?
7) A 5 kg projectile has a velocity of 255 m/s to the right. What force is required to stop this projectile in 1.45 s?
8) How much time would it take for a 0.17 kg ice hockey puck to decrease its speed by 9.0 m/s if the coefficient
of kinetic friction between the ice and the puck is 0.050?
9) The surface of Jupiter’s moon Europa is covered with ice. Suppose an ice boat moving with a speed of
14.5 m/s drifts to a stop. The boat’s mass is 1.50 × 103 kg and the coefficient of kinetic friction between the
boat’s runners and the ice is 0.065. However, free-fall acceleration on Europa is only 1.305 m/s2. a) How long
will it take the boat to stop? b) How far does the ice boat glide before stopping?
Chapter 7 Answers:
1) 181 N
2) a) 7000 N b) 6250 N c) No.
3) 329 m/s
10) 0.89 m from the male seal (2.11 m from the female seal)
4) 4.96 × 10 15 kg
5) 52 m
6) 80.6 kg
7) 25.8 km
8) 5.9 m
9) 879 N
Physics A
Chapter 7 - Circular Motion, Gravity & Torque
1) A 45 kg child riding a Ferris wheel has a tangential speed of 8.5 m/s. Find the magnitude of the centripetal
force on the child if the distance from the child to the axis of the wheel is 18 m.
2) An automobile with a tangential speed of 14 m/s follows a circular road that has a radius of 35.0 m. The
pavement is wet and oily, so the coefficient of kinetic friction between the car’s tires and the pavement
is only 0.500. a) How large is the centripetal force needed to maintain the car’s circular motion? b) How large
is the available frictional force? c) Is the available frictional force large enough to maintain the automobile’s
circular motion? Assume the automobile has a mass of 1250 kg.
3) A small asteroid with a mass of 2.05 × 108 kg is pulled into a circular orbit around Earth. The distance from
the asteroid to Earth’s center is 7378 km. If the gravitational force needed to keep the asteroid in orbit
has a magnitude of 3.00 × 109 N, what is the asteroid’s tangential speed?
4) Deimos, a satellite of Mars, has an average radius of 6.3 km. If the gravitational force between Deimos and a
3.0 kg rock at its surface is 2.5 × 10–2 N, what is the mass of Deimos?
5) The largest diamond ever found has a mass of 0.621 kg. If the force of gravitational attraction between this
diamond and a person with a mass of 65.0 kg is 1.0 × 10–12 N, what is the distance between them?
6) In 1989, a cake with a mass of 5.81 × 104 kg was baked in Alabama. Suppose a cook stood 25.0 m from the
cake. The gravitational force exerted between the cook and the cake was 5.0 × 10−7 N. What was the cook’s
mass?
7) The passenger liners Carnival Destiny and Grand Princess, built recently, have a mass of about 1.0 × 108 kg
each. How far apart must these two ships be to exert a gravitational attraction of 1.0 × 10−3 N on each other?
8) The pterosaur was the most massive flying dinosaur. The average mass for a pterosaur has been estimated
from skeletons to have been between 80.0 and 120.0 kg. The wingspan of a pterosaur was greater than 10.0 m.
Suppose two pterosaurs with masses of 80.0 kg and 120.0 kg sat on the middle and the far end, respectively, of
a light horizontal tree branch. The pterosaurs produced a net counterclockwise torque of 9,400 Nm about the
end of the branch that was attached to the tree. What was the length of the branch?
9) The heaviest sea sponge ever collected had a mass of 40.0 kg, but after drying out, its mass decreased to
5.4 kg. Suppose two loads equal to the wet and dry masses of this giant sponge hang from the opposite ends of
a horizontal meterstick of negligible mass and that a fulcrum is placed 70.0 cm from the larger of the two
masses. How much extra force must be applied to the end of the meterstick with the smaller mass in order to
provide equilibrium?
10) The Galápagos fur seals are very small. An average adult male has a mass of 64 kg, and a female has a mass
of only 27 kg. Suppose one average adult male seal and one average adult female seal sit on opposite ends of a
light board that has a length of 3.0 m. How far from the male seal should the board be pivoted in order for
equilibrium to be maintained?
Chapter 6 Answers:
1) 6.66 m/s, south
2) 800 kg•m/s
8) 18 seconds
9) a) 171 seconds
3) 18.5 m/s
b) 1242 m
4) 3.38 × 10 31 kg
5) 12.5 m/s
6) 0.496 m/s, left
7) 879 N