Topics: Dynamics
Date: 23.04.2021
1) (a)Calculate the momentum of a 110-kg football player running at 8.00 m/s. (b) Compare the
player’s momentum with the momentum of a hard-thrown 0.410-kg football that has a speed of
25.0 m/s.
2) During the 2007 French Open, Venus Williams hit the fastest recorded serve in a premier
women’s match, reaching a speed of 58 m/s (209 km/h). What is the average force exerted on the
0.057-kg tennis ball by Venus Williams’ racquet, assuming that the ball’s speed just after impact is
58 m/s, that the initial horizontal component of the velocity before impact is negligible, and that
the ball remained in contact with the racquet for 5.0 ms (milliseconds)?
3) Hold a tennis ball side by side and in contact with a basketball. Drop the balls together. (Be
careful!) What happens? Explain your observations. Now hold the tennis ball above and in contact
with the basketball. What happened? Explain your observations. What do you think will happen if
the basketball ball is held above and in contact with the tennis ball?
4) Find a few ice cubes which are about the same size and a smooth kitchen tabletop or a table
with a glass top. Place the ice cubes on the surface several centimeters away from each other. Flick
one ice cube toward a stationary ice cube and observe the path and velocities of the ice cubes after
the collision. Try to avoid edge-on collisions and collisions with rotating ice cubes. Have you
created approximately elastic collisions? Explain the speeds and directions of the ice cubes using
momentum.
5) Which has more mass: a kilogram of cotton balls or a kilogram of gold?
6) What Acceleration Can a Person Produce when Pushing a Lawn Mower?
Suppose that the net external force (push minus friction) exerted on a lawn mower is 51 N (about
11 lb) parallel to the ground. The mass of the mower is 24 kg. What is its acceleration?