physics ch 7 test

recoil is noticeable if we throw a heavy ball while standing on roller skates. if instead we go through the motions of throwing the ball but hold onto it, what will our net recoil velocity be

0

two freight cars having the same mass and speeds move toward each other on a track and sit together. after the collision, the velocity of the freight cars will be what

0

When can a collision be considered elastic

1) no sound 2) no deformation 3) when objects don't get hot 4) objects have same shape after collision

if the momentum of an object changes and its mass remains constant, what can you say about its velocity, acceleration, and forces acting on it

1) velocity is changing 2) it's accelerating 3) there's a force acting on it

how could you increase the final momentum of a tennis ball

1)increase the force 2) increase contact time 3) follow through 4) swing as hard as possible

why are automobile dashboards padded

so that if you hit them, you will have a less impact because the time is lengthened

an astronaut is at rest in space when he throws a rock that has more mass than he does which moves faster

the aastronaut

a boxing expert executes a swift blow and punches his opponent. how does the impulse on both the block and the experts hand compare, the forces, and the time of impact

they are all the same

if a potato launcher is fired straight up into the air, compared to the force on the potato, what is the force on the gun

they are equal

if a potato launcher is fired straight up into the air, compared to the impulse on the potato, what is the impulse on the gun

they are the same

a boxing expert executes a switft blow and punches his opponent. how does the impulse on both the block and the expert's hand compare the forces the time of impact

they will all be the same

suppose a man is standing on a frictionless surface. in order to get off this frictionless surface, what must the man do

throw something in the direction opposite to that in which he wants to go

suppose a man is standing on a frictionless surface. In order to get off this frictionless surface what does the man have to do

throw something in the opposite direction he wants to go

a 5kg chunk of clay moving at 10 m/s collides with and sticks to a 10 kg boulder that is initially at rest. the boulder with its clay host will then be set in motion with what momentum?

5(10) + (10)0 = x x = 50 kg*m/s

when Reggie Jackson stepped up to the plate and hit a 0.150 - kg fast ball traveling at 36.0 m/s, the impact caused the ball to leave his bat with a velocity of 45.0 m/s in the opposite direction. If the impact lasted for 0.002 s, what force did Jackson exert on the baseball?

(0.150)(-81) = f(0.002) f = -6000 N

a Shuttle astronaut is sent to repair a defective relay in a 600.00 - kg satellite that is traveling in space at 17,000.0 m/s away. Suppose the astronaut and his Manned Maneuvering Unit (MMU) have a mass of 400.00 kg and travel at 17,010.0 m/s toward the satellite. What is the combined velocity when the astronaut grabs hold of the satellite?

(600)(17,000) + (400)(17,010) = (600+400)x x = 17004 m/s

a 300. - kg motorboat is turned off as it approaches a dock and it coasts in toward the dock at 0.50 m/s. Isaac, whose mass is 62.0 kg, jumps off the front of the boat with a speed of 3.0 m/s relative to the boat. What is the velocity of the boat after Isaac jumps?

(62+300)0.50 = x(300) + (3.0)62 -5 = 300x x = -.017 m/s

about 50,000 years ago, in an area located outside Flagstaff, Arizona, a giant 4.5 x 107 - kg meteor fell and struck the earth, leaving a 180-m-deep hole now known as Barringer crater. If the meteor was traveling at 20,000 m/s upon impact, with what average force did the meteor hit the earth?

Vav = (20,000 + 0) / 2 = 10,000 10,000 = 180 / t t = .018 p = 4.5x10^7 (20,000) = f(0.018) f = 5 x 10^13 N

The U.S. Army's parachuting team, the Golden Knights, is on a routine jumping mission over a deserted beach. On a jump, a 65 - kg Knight lands on the beach with a speed of 4.0 m/s, making a 0.20 - m deep indentation in the sand. With what average force did the parachute hit the sand?

Vav = (4.0+0) / 2 = 2 2 = 0.20 / t t = 0.1 s p = (65)(4.0) = 260 f = 260 / 0.1 = 2,600 N

which has more momentum, a mac truck moving at 15 miles per hour or a mustang moving at 15 miles per hour why

a mac truck because it has more mass

the amount of force of a ball hitting the ground depends upon what factors

air resistance falling speed time of impact if it bounces

the amount of force on a ball hitting the ground depends upon what factors (4)

air resistance, falling speed, time of impact, if it bounces

Define momentum

an objects mass times its velocity

if an astronaut is at rest in space when he throws a rock that has more mass than he does, which moves faster, the astronaut or the rock

astronaut - same force, less mass

in order to catch a basketball, a player moves his or her hands backward in the direction of the ball's motion. why does this reduce the force of impact on the player's hand

because the time of impact is longer

if a car is traveling along the highway and needs a certain amount of force to stop, will more or less stopping force be required when the car has more mass more momentum more stopping distanct

care has more mass, more stopping force is required more momentum means more stopping force more stopping distance means less stopping force

compared to a wagon moving at 30 miles per hour, the same wagon moving at 60 miles per hour has how much momentum

double the momentum

what must an object have in order to have a very large momentum

either a high mass or a high velocity or both

what must an object have in order to have a very large momentum

either a very large mass, a very fast speed or both

what type of collision is one where two objects collide and completely bounce apart with no lasting deformation or generation of heat

elastic

assuming all other variables are kept constant, what type of collision has the greatest speed after the collision, an elastic or inelastic

elastic because they bounce apart

assuming all other variables are kept constant, what type of collision has the greatest speed after the collision, an elastic one or an inelastic one

elastic same forces on two smaller masses instead of one large mass

define impulce

force per time interval

a ping-pong ball moving forward with 8 units of momentum strikes and bounces backward off a heavy ball that is initially at rest and free to move. the heavy ball is set in motion with a momentum of what

greater than 8 because the ping pong ball bounces

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 what

half as large

a moving freight car turns into an identical car at rest on the track. the cars couple together. compared to the velocity of the first care before the collision, the velocity of the combined cars after the collision will be what

half of the first

what role does follow through play in the hitting of a baseball

hurts the batter less because the time of impact is longer

the momentum change of an object is always equal to what

impulse

why does a bullet shot from a long-barrel gun travel faster than one shot from a short-barrel gun

impulse is greater on long-barrel due to a longer time of impact

why are padded walls used around the track

increase the time of impact in a collision

why are padded walls used around the track on nascar racetracks

increase time of impact

how could you increase the final momentum of a tennis ball

increasing the force or acceleration

what type of collision is one where two objects collide and completely stick together

inelastic

in order to catch a basketball, a player moves his or her hands backward in the direction of the ball's motion. why does this reduce the force of impact on the players hand

it increases the impact time

if a moving object continues along a straight line path and its mass is doubled without changing its velocity, what will happen to its momentum

it will double

if a moving object continues along a straight line path and it's mass double without changing its velocity, what will happen to it's momentum

it would double

what is momentum measured in

kg*m/s

are impulses normally smaller or large when bouncing takes place

larger because the time is lengthened

are impulses normally smaller or larger when bouncing takes place

larger there is a larger change in velocity

a ball is moving at 6 m/s and has a momentum of 36 kg m/s. what is the ball's mass

m = 36 / 6 = 6 kg

define momentum

mass times velocity

a snail moving with 1 unit of momentum hits a sticks to a heavy pebble that is initially at rest. after the small sticks, how does the final momentum compare to the original momentum of both the snail and the pebble

momentum is conserved so 1 unit

A snail moving with 1 unit of momentum hits and sticks to a heavy pebble that is initially at rest. After the snail sticks to the pebble, how does the final combined momentum compare to the original momentums of both the snail and the pebble?

momentum is conserved so it will still be 1 unit

if a car is traveling along the highway and needs a certain amount of force to stop, will more or less stopping force be required when the car has more mass, more momentum, or more stopping time

more more less

if the net external force acting on a system is zero, does it mean that there is no momentum in the system at all

no because there can be momentum on the individual objects

a gun fires a potato. will the speed of the potato be the same as the speed of the recoiling gun why or why not

no because they have different masses

when can a collision be considered elastic

no deformation no sound no heat same shape before and after

is momentum a scalar quantity

no it is a vector quantity because it is measured in both direction and magnitude

a gun fires a potato, will the speed of the potato be the same as the speed of the recoiling gun

no the gun and the potato have different masses

if the net external force acting on a system is zero, does it mean that there is no momentum in the system at all

no there still may be momentum left in the system

is momentum a scalar quantity

no, momentum is a vector quantity because it has both direction and magnitude

a 4 N bowling ball falls to the ground. what impact force does it hit the ground with

not enough info to answer

an 8kg ball is thrown at 10 m/s, what is the ball's momentum

p = 8*10 = 80 kg m/s

a regular tennis ball and a cement filled tennis ball are dropped simultaneously from a tower and they the ground at the same time. why do they hit the ground at the same time

the cement ball has more momentum, but the same amount of gravity acts on both objects

a regular tennis ball and a cement filled tennis ball are dropped simultaneously from a tower and they reach the ground at the same time. why do they hit the ground at the same time

the cement filled ball has a higher momentum, but the same amount of gravity acts on both balls

what roll does follow through play in the hitting of a baseball

the contact time with the ball is longer, increasing the impulse

the force that accelerates a rocket into outer space is exerted on the rocket by what

the exhaust gases

define impulse

the force exerted on an object times the time it lasts

suppose a rifle is made of a strong but very light material. suppose also that the bullet is more massive than the gun itself. What would happen if such a weapon were fired

the gun would be shot backward faster than the bullet would be shot forward

suppose a rifle is made of a strong but very light material. suppose also that the bullet is more massive than the gun itself. what would happen if such a weapon were fired why

the gun would shoot backward with a greater speed than the bullet would have going forward

the momentum change of an object is always equal to what

the impulse acting on it

a small car and a large truck are pushed from rest across a parking lot, equal distances with equal forces. which vehicle receives the greater impulse

the large truck

A ping-pong ball moving forward with 8 units of momentum strikes and bounces backward off a heavy ball that is initially at rest and free to move. The heavy ball is set in motion with a momentum of what? (compared to the momentum of the ping-pong ball

the momentum of the heavy ball will be greater than 8 units because the ping pong ball bounces

a rifle recoils from firing a bullet. why is the speed of the rifle's recoil small compared to the speed of the bullet

the rifle has a lot more mass

a rifle recoils from firing a bullet. why is the speed of the rifle's recoil small compared to the speed of the bullet

the rifle has more mass

if a potato launcher is fired straight up into the air, compared to the force on the potato, what is the impulse on the gun

the same

when a potato launcher is fire straight up into the air, compared to the impulse on the potato, what is the impulse on the gun

the same

small car and a large truck are pushed from rest across a parking lot, equal distance with equal forces which vehicle receives the greater impulse

the truck

which has more momentum, a mac truck moving at 15 mph or a mustang moving at 15 mph

the truck because it has more mass

why does a bullet shoot from a long barrel gun travel faster than one shot from a short barreled gun

there is a longer time of impact

When a basketball player lands after a jump, he usually bends his knees as he reaches the ground. By doing this, what happens to the time of the impact compared to what it would be in a stiff-legged landing? If the impact time is about 10 times more, by how much will the average force on your body be reduced by?

time of impact is increased the force is reduced by 10

why are automobile dashboards padded

to increase the time of impact on the collsision

compared to a wagon moving at 30 mph the same wagon moving at 60 mph has what momentum

twice as much

a 15 kg ball has a momentum of 24 kg m/s. what is the ball's speed

v = 24/15 = 1.6 m/s

if the momentum of an object changes and its mass remains constant, what can you say about its velocity, acceleration, and the forces acting on it

velocity changes it is accelerating there is a force acting

when is the momentum of a system conserved

when there is no net force or no net impulse

are perfectly elastic collisions between large objects uncommon the everyday world

yes

are perfectly elastic collisions between large objects uncommon in the everyday world

yes because some heat is generated

if a net forces acts on a system, will the system's momentum change

yes, a net force means a change in velocity which will change the momentum

if a net force acts on a system, will the system's momentum change

yes, a net force means change in velocity which means change in momentum

Recoil is noticeable if we throw a heavy ball while standing on roller skates. If instead we go through the motions of throwing the ball but hold onto it, what will our net recoil velocity be?

zero

two frieght cars having the same mass and speeds move toward each other on a track and stick together after the collision the velocity of the freight cars will be what

zero