Momentum
Two gliders having the same mass and speed move toward each other on an air track and stick together. After the collision, the velocity of the gliders is
0
Momentum
An object's mass times its velocity.
An unfortunate bug splatters on the windshield of a moving car. Describe the forces, impulses, momentum changes, and accelerations of both the bug and the car.
If a bug splatters on the windshield of a moving car, their forces will be equal but in opposite directions. The impulses will be equal and in opposite directions. The momentum change will be equal for the car and bug. The bug will have greater acceleration than the car because it has a smaller mass.
When you jump off a step, you usually bend your knees as you reach the ground. By doing this, the time of the impact is about 10 times more what it would be in a stiff-legged landing, and the average force on your body is reduced by
about 10 times.
A cannon recoils from launching a cannonball. The speed of the cannon's recoil is small because the
cannon has far more mass than the cannonball.
While roller-skating, Granny collides with her tiny grandson Ambrose who is at rest. Ignoring any friction effects, Ambrose's speed after the collision will be greatest when
he and Granny make a bouncing collision, each going in opposite directions.
A cannonball shot from a long-barrel cannon travels faster than one shot from a short-barrel cannon because the cannonball receives a greater
impulse.
In order to increase the final momentum of a golf ball, we could
increase the force acting on it, follow through when hitting the ball, increase the time of contact with the ball, swing as hard as possible.
The reason padded dashboards are used in cars is that they
increase the time of impact in a collision.
The momentum of an object is defined as the object's
mass times its velocity.
Two objects, A and B, have the same size and shape, but A is twice as heavy as B. When they are dropped simultaneously from a tower, they reach the ground at the same time, but A has a higher
momentum
A meteor that originally was heading south breaks up into two chunks. One of the chunks moves southwest. The second chunk was not immediately found, but scientists guessed that they should look for an object heading
southeast
Recoil is noticeable if you throw a heavy ball while standing on roller skates. If instead you go through the motions of throwing the ball but hold onto it, your net recoil velocity will be
0
A 1-N apple falls to the ground. The apple hits the ground with an impact force of
1 N
A 5-kg blob of clay moving horizontally at 4 m/s has a head-on collision with a 4-kg blob of clay that moves toward it at 2 m/s. What is the speed of the two blobs stuck together immediately after the collision?
1.3 m/s
An 8-kg blob of clay moving horizontally at 2 m/s hits a 3-kg blob of clay at rest. What is the speed of the two blobs stuck together immediately after the collision?
1.5 m/s
A railroad diesel engine coasting at 12 km/h runs into a stationary flatcar. The diesel weighs 5 times as much as the flatcar. Assuming the cars couple together, how fast are they moving after the collision?
10 km/h
Assume that a 15-kg ball moving at 8 m/s strikes a wall perpendicularly and rebounds elastically at the same speed. What is the amount of impulse given to the wall?
240 N*s
A 10-kg cement block moving horizontally at 6 m/s plows into a bank of sand and comes to a stop in 2 s. What is the average impact force on the bank?
30 N
A ball is moving at 6.0 m/s and has a momentum of 24.0 kg·m/s. What is the ball's mass?
4.0 kg
A loaded freight car has 5 times as much mass as an empty freight car. If the loaded car coasts at 5 m/s and collides with and attaches to the empty car at rest, what will be the speed of both cars after collision?
4.2 m/s
A 10-kg bowling ball moving at 4 m/s bounces off a spring at about the same speed that it had before bouncing. What is the change in momentum of the bowling ball?
80 kg*m/s
A boy fires a table tennis ball launcher. Briefly describe the forces and impulses on the launcher and the ball. Which has more momentum? Which is moving faster? Explain.
The forces and impulses of the tennis ball and launcher will be equal but in opposite directions. They will have equal momentum changes. The ball is less in mass so it will have the greater acceleration.
A karate expert executes a swift blow and splits a cement block with her bare hand.
The forces on both the block and the expert's hand have the same magnitude, The times of impact on both the block and the expert's hand are the same, The impulses on both the block and the expert's hand have the same magnitude.
Which has more momentum, a large truck moving at 30 miles per hour or a small truck moving at 30 miles per hour?
The large truck
A truck travels north with a momentum of 2,600 kg·km/s, and a motorcycle heads west with a momentum of 1,500 kg·km/s. The motorcycle hits the truck. If the two vehicles collide and then stick together, what is the momentum and direction of travel?
The vehicles travel with a momentum of 3,000 kg·km/s in the NW direction.
A cement truck of mass 16,000 kg moving at 15 m/s slams into a cement wall and comes to a halt. What is the force of impact on the truck?
There isn't enough information. I need the time interval.
T/F? Automobile dashboards that are padded lengthen the time of impact in case of a collision.
True
T/F? If a net force acts on a system, the system's momentum will change.
True
T/F? When two objects collide and stick together, the collision is said to be inelastic.
True
What does it mean to say that momentum is conserved? Give at least two examples where momentum is conserved in a collision.
When momentum is conserved, that means the quantity does not change. Examples of momentum being conserved are cars colliding and stars exploding.
A freight train rolls along a track with considerable momentum. If it were to roll at the same speed but had twice as much mass, its momentum would be
doubled
A cannon fires a cannonball. The speed of the cannonball will be the same as the speed of the recoiling cannon
if the mass of the cannonball equals the mass of the cannon.
The momentum change of an object is equal to the
impulse acting on it.
A moving freight car runs into an identical car at rest on the track. The cars couple together. Compared to the velocity of the first car before the collision, the velocity of the combined cars after the collision is
one half as large.
Suppose an astronaut in outer space wishes to toss a ball against a very massive and perfectly elastic concrete wall and catch it as it bounces back. If the ball is as massive as the astronaut, then
the astronaut will never catch the first bounce.
A table tennis ball launcher is fired. Compared to the force on the ball, the force on the launcher is
the same
A 70-kg free-floating astronaut fires 0.10-kg of gas at a speed of 30 m/s from her propulsion pistol. What is the astronaut's recoil speed?
0.04 m/s
A piece of putty moving with 2 units of momentum strikes and sticks to a heavy bowling ball that is initially at rest. After the putty sticks to the ball, both are set in motion with a combined momentum that is
2 units
A 40-kg football player leaps through the air to collide with and tackle a 50-kg player heading toward him, also in the air. If the 40-kg player is heading to the right at 9 m/s and the 50-kg player is heading toward the left at 2 m/s, what is the speed and direction of the tangled players?
2.89 m/s to the right
A 50-kg cart moving at 100 km/h collides head-on with an approaching 50-kg cart moving at 10 km/h (in the opposite direction). If the two carts stick together, what will be their speed?
45 km/h
A 30-kg girl and a 50-kg boy face each other on friction-free roller skates. The girl pushes the boy, who moves away at a speed of 3 m/s. What is the girl's speed?
5.0 m/s
A 4.0-kg ball has a momentum of 20.0 kg·m/s. What is the ball's speed?
5.0 m/s
A 5.0-kg chunk of putty moving at 10.0 m/s collides with and sticks to a 7.0-kg bowling ball that is initially at rest. The bowling ball with its putty passenger will then be set in motion with a momentum of
50.0 kg·m/s.
A 2-kg ball is thrown at 3 m/s. What is the ball's momentum?
6 kg·m/s
If all people, animals, trains and trucks all over the world began to walk or run towards the east, then
Earth would spin a bit slower.
T/F? If the net external force acting on a system is zero, then the total momentum of the system is zero.
False
T/F? Impulses are normally smaller when bouncing takes place.
False
T/F? Momentum is NOT conserved when interacting objects don't move along the same straight line.
False
T/F? Momentum is a scalar quantity.
False
In terms of momentum change, explain why it is best to "give" when catching a baseball. Provide other examples of situations in which you want to lengthen the impact time in a collision.
It is best to "give" when catching a baseball because lengthing the time of impact reduces the force. Other times you may want to lengthen the impact time in a collision is a bicycle or car collision or hitting a baseball.
A table tennis ball moving forward with 5 units of momentum strikes and bounces backward off a heavy bowling ball that is initially at rest and free to move. The bowling ball is set in motion with a momentum of
More than 5 units
Superman is at rest in space when he throws an asteroid that has more mass than he does. Which moves faster, Superman or the asteroid?
Superman
A piece of putty and a rubber ball have the same mass. If you drop them from the same height, which object will produce a greater impulse and why?
The rubber ball will produce a greater impulse because it will bounce.
T/F? Perfectly elastic collisions between large objects are uncommon in the everyday world.
True
T/F? When a baseball player follows through in hitting the ball, the contact time with the ball is longer.
True
T/F? When two objects collide and completely bounce apart with no lasting deformation or generation of heat, the collision is said to be elastic.
True
If the momentum of an object changes and its mass remains constant,
it is accelerating (or decelerating), there is a force acting on it, its velocity is changing.
A car traveling along the highway needs a certain amount of force exerted on it to stop. More stopping force may be required when the car has
less stopping distance, more momentum, more mass.
A small economy car (low mass) and a limousine (high mass) are pushed from rest across a parking lot, equal distances with equal forces. The car that receives the greater impulse is the
limousine
The force that accelerates a rocket into outer space is exerted on the rocket by
the exhaust gases.
Impulse
the force exerted on an object times the time it lasts.
A table tennis ball launcher is fired. Compared to the impulse on the ball, the impulse on the launcher is
the same
The force of an apple hitting the ground depends upon
the speed of the apple just before it hits, the time of impact with the ground, whether or not the apple bounces, air resistance on the apple as it falls.
Suppose a cannon is made of a strong but very light material. Suppose also that the cannonball is more massive than the cannon itself. For such a system
the target would be a safer place than where the operator is located.
In order to catch a ball, a baseball player moves his or her hand backward in the direction of the ball's motion. Doing this reduces the force of impact on the player's hand principally because
the time of impact is increased.
A collision is considered elastic if
there is no lasting deformation, the objects don't stick together, the objects that collide don't get warmer, after the collision, the objects have the same shape as before the collision.
Momentum of a system is conserved only when
there is no net external force acting on the system.
Suppose a girl is standing on a pond where there is no friction between her feet and the ice. In order to get off the ice, she can
throw something in the direction opposite to the way she wants to go.
Compared to a sports car moving at 30 miles per hour, the same sports car moving at miles per hour has
twice as much momentum.