Conservation of Momentum and
Collision
Kimal Honour Djam
ASFA
A child jumps from a small boat to a dock. Why does she have to
jump with more effort than she would need if she were jumping
through an identical displacement, but from a boulder to a tree
stump?
A 5.0-kg object and a 10-kg object, both resting on a
frictionless table, are connected by a massless
compressed spring. The spring is released and the
objects fly off in opposite directions. The 5.0-kg object
has a velocity of 8.0 m/s to the left. What is the velocity
of the 10-kg object?
A 0.060-g handball is thrown straight toward a wall with a speed of
10 m/s. It rebounds straight backward at a speed of 8.0 m/s.
(a) What impulse is exerted on the wall?
(b) If the ball is in contact with the wall for 3.0 ms, what
average force is exerted on the wall by the ball?
(c) The rebounding ball is caught by a player who brings it to rest. In the
process, her hand moves back 0.50 m. What is the impulse received by the player?
(d) What average force was exerted on the player by the ball?
A 2000-kg car traveling to the right at 30 m/s is chasing a second car of the same
mass that is traveling in the same direction at 10 m/s.
(a) If the two cars collide and stick together, what is their speed just after the
collision?
(b)What
fraction of the initial kinetic energy of the cars is lost during
this collision? Where does it go?
A 5.0-kg object with a speed of 4.0 m/s collides head-on with a 10-kg
object moving toward it with a speed of 3.0 m/s. The 10-kg object
stops dead after the collision. (a) What is the post collision speed of
the 5.0-kg object? (b)Is the collision elastic?
A 2.0-kg block moving to the right with a speed of 5.0 m/s collides
with a 3.0-kg block that is moving in the same direction at 2.0
m/s. After the collision, the 3.0-kg block moves to the right at 4.2
m/s. Find the velocity of the 2.0-kg block after the collision
HOMEWORK
•
You kick a soccer ball whose mass is 0.43 kg. The ball leaves your foot with an
initial speed of 25 m/s.
(a) What is the magnitude of the impulse associated with the force of your
foot on the ball?
(b) If your foot is in contact with the ball for 8.0 ms, what is the magnitude
of the average force exerted by your foot on the ball?
•
A 0.15-kg baseball traveling horizontally is hit by a bat and its direction is exactly
reversed. Its velocity changes from +20 m/s to -20 m/s.
(a) What is the magnitude of the impulse delivered by the bat to the ball?
(b) If the baseball is in contact with the bat for 1.3 ms, what is the average
force exerted by the bat on the ball?
• A 3.0-kg block moving at 4.0 m/s has a head-on elastic collision with a stationary
block of mass 2.0 kg. Use conservation of momentum and the fact that the relative
speed of recession equals the relative speed of approach to find the velocity of
each block after the collision. Check your answer by calculating the initial and final
kinetic energies of each block.