Physics Chapter 7 Study Guide
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
After a firecracker falling through the air explodes, the net momentum of its fragments decreases.
false
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
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
The cannonball launched from a cannon with a long barrel will be faster because the cannonball receives a greater
impulse
The momentum change of an object is equal to the
impulse acting on it
The reason padded dashboards are used in cars is that they
increase the time of impact in a collision
A golf ball moving forward with 1 unit 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
less than 1 unit
A small economy car (low mass) and a limousine (high mass) are pushed from rest across a parking lot, equal distance with equal forces. The car that receives the greater impulse is the car
limousine
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
Momentum of a system is conserved only when
there is no net external force acting on the system
If a net force acts on a system, the system's momentum will change.
true
Impulse is defined as the force exerted on an object times the time it lasts.
true
Momentum is defines as an object's mass times it velocity
true
Perfectly elastic collisions between large objects are uncommon in the everyday world
true
The padding on car dashboards lengthens the time of a passenger's impact during a collision.
true
When two objects collide and completely bounce apart with no lasting deformation or generation of heat, the collision is said to be elastic
true
When two objects collide and completely stick together, the collision is said to be inelastic.
true
Compared to a sports car moving at 30 miles per hour, the same sports car moving at 60 miles per hour has
twice as much 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
zero
A 4-kg ball has a momentum of 12 kg m/s. What is the ball's speed?
3 m/s
A 10-kg cement block moving horizontally at 2.0 m/s plows into a pillow and comes to a stop in 0.5 s. What is the average impact force on the pillow
40
A 2-kg ball is thrown at 3 m/s. What is the ball's momentum
6 kg m/s
What is the average momentum of a 70-kg runner who covers 400 m in 50 s?
70x400 =28,000/50 =560 kg x m/s
A railroad diesel engine coasting at 10 km/h runs into a stationary flatcar. The diesel weighs 4 times as much as the flatcar. Assuming the cars couple together, how fast are they moving after the collision.
8 kmh
A 8.0-kg blob of clay moving horizontally at 2.0 m/s hits a 4.0 kg blob of clay at rest. What is the speed of two blobs stuck together immediately after the collision
8kg x 2.0 m/s + 4 x 0 = 8kg + 4gk
Which of the following has the largest momentum
A pickup truck traveling down the highway
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
A piece of putty moving with 1 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
The rubber ball will produce a greater impulse because it will bounce
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 100 times
If the momentum of an object changes and its mass remains constant
all of the above (velocity changes, it is accelerating, force acting on it)
Skelly the skater traveling at high speed needs a certain amount of force to stop him. More stopping force will be needed if he has
all of these (more mass/momentum, less stopping distance)
If the net force acting on a system is zero, then the total momentum of the system is zero
false
While rollerblading, 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
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
A 40 kg football player leaps through the air to collide with and tackle a 60 kg player heading toward him, also in the air. If the 40 kg player is heading to the right at 7.0 m/s, and the 60 kg player is heading toward the left at 3.0 m/s, what is the speed and direction of the tangled players
(40)(7)+(60)(3)=(40+60)= 1m/s
A 5.0 kg blob of clay moving horizontally at 2.0 m/s has a head on collision with a 6.0 kg blob of clay that moves toward it at 1.0 m/s. What is the speed of the two blobs stuck together immediately after the collision
(5*2)+6*-1)=11x x=0.63
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-kg chunk of putty moving at 1 m/s collides with and sticks to a 5-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
0.17
A 1-N apple falls to the ground. The apple hits the ground with an impact force of about
1 N
A 30-kg girl and a 25-kg boy face each other on friction-free roller skates. The girl pushes the boy, who moves away at a speed of 1.0 m/s. What is the girl's speed?
1.6 m/s
A ball is moving at 4 m/s has a momentum of 48 kg m/s. What is the ball's mass
12 kg
If Superman at rest in free space throws an asteroid that has more mass than Superman, then which moves faster?
Superman
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
all of the above
A collision is considered elastic if
all of the above
A karate expert executes a swift blow and severs a cement block with her bare hand.
all of the above
If the momentum of an object changes and its mass remains constant
all of the above
In order to increase the final momentum of a golf ball, we could
all of the above
The forces of an apple hitting the ground depends upon
all of the above
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
If the net external force acting on a system is zero, then the total momentum of the system is zero.
false
Impulses are normally smaller when bouncing takes place
false
Impulses are smaller when bouncing takes place.
false
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
get on her hands and knees and crawl off the ice
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 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
not enough information
A moving freight car runs into an identical car at rest on the track The car couple together. Compared to the velocity of the first car before the collision, the velocity of the combined car after the collision is
one half as large
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
Suppose an astronaut in outer space wishes to play a solitary "throw, bounce, and catch" game by tossing a ball against a very massive and perfectly elastic concrete wall. If the ball is as massive as the astronaut, then
the astronaut will never catch the first bounce
The force that accelerates a rocket in outer space is exerted on the rocket by the
the exhaust gases
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 Ping-Pong ball launcher is fired. Compared to the force on the ball, the force on the launcher is
the same
A Ping-Pong ball launcher is fired. Compared to the impulse on the ball, the amount of impulse on the launcher is
the same
A Ping-Pong ball launcher is fired. Compared to the impulse on the ball, the impulse on the launcher is
the same