Physical Science exam #3
a 5000 kg freight car crashes into a 10,000 kg freight car at rest. they couple upon collision and move with a speed of 2 m/s. what was the initial speed of the 5000 kg freight car
6 m/s
the greater effciency with the curved blades of a pelton wheel is due to
bouncing
the impulse momentum relationship is a direct result of
newtons second law
When a boxer moves into an oncoming punch, the force experienced is
increased
according to the impulse momentum relationship ft= change in mv, a falling bungee jumper has momentum which is reduced by the force F exerted by the bungee cord. if v is the speed of the jumper, then m in the equation is the mass of the
jumper
If a charging rhinoceros has momentum, it must also have
kinetic energy.
jogging jake runs along the top of a moving flatcar in the direction of motion of the flatcar. if he runs in the opposite direction, the combined momentum of jake and the flatcar relative to a observer at rest will be
less
A melon is projected into the air with 100 J of kinetic energy in the presence of air resistance. When it returns to its initial level its kinetic energy is
less than 100 J.
An object may have potential energy because of its
location
When you can't escape being hit by a fast-moving object, you'll suffer a smaller force if the collision time is
long
a karate expert executes a swift blow and breaks a cement block with her bare hand. the magnitude of the force on her hand is
the same as the force applied to the block
Just after a big fish swallows a small fish, the momentum of the two-fish system is
the same before and after lunch
When a boxer is moving away from a punch, the force experienced is reduced because
the time of contact is increased
the conservation of momentum is most closely related to newtons
third law
A shopping cart moves with a kinetic energy of 40 J. If it moves at twice the speed, its kinetic energy is
160j
a peice of putty moving with 1 unit of momentum strikes and sticks to a heavy bowling ball initially rest. after the putty sticks to the ball, both move with a combined momentum of
1 unit
Two billiard balls having the same mass roll toward each other at the same speed. What is the net momentum of the two-ball system?
0 kg m/s
When a 100-kg astronaut ejects 0.1 kg of gas at a speed of 50 m/s from her propulsion pistol, her recoil speed is
0.05 m/s
a 2 kg rifle is horizontally suspended by a pair of strings so that recoil can be measured. the rifle fires a 0.001 kg bullet at a speed of 200 m/s. the recoil velocity of the rifle is about
0.1 m/s
Two identical freight cars roll without friction towards each other on a level track. One car rolls at 2 m/s and the other car rolls at 1 m/s. After the cars collide, they couple and roll together with a speed of
0.5 m/s
a 30 kg girl on friction-free roller blades pushes away a 25 kg boy also on rollerblades at 1 m/s. the girls speed is
0.83 m/s
a 1 kg chunk of putty moving at 1 m/s collides and sticks to a 5 kg bowling ball initially at rest. the bowling ball and putty move with a momentum of
1 kg m/s
Two identical gliders slide toward each other on an air track. One moves at 1 m/s and the other at 2 m/s. They collide, stick, and moves at
1/2 m/s
a 1kg glider and a 2kg glider both slide toward each other at 1 m/s on an air track. when they collide and stick, the combined-glider spped is
1/3 m/s
Consider gliders that slide friction-free along a horizontal air track. Glider A has a mass of 1 kg, a speed of 1 m/s, and collides with glider B, which has a mass of 5 kg and is at rest. If they stick upon collision the speed the combined gliders will be
1/6 m/s
a 1 kg chunk of putty moving at 1 m/s collides and sticks to a 5 kg bowling ball that is initially at rest in space. the bowling ball and putty are then set in motion with a speed of
1/6 m/s
a 5 kg fish swimming 1 m/s swallows an absent-minded 1 kg fish swimming toward it at 4 m/s. the speed of the larger fish after lunch is
1/6 m/s
A melon is tossed straight upward with 100 J of kinetic energy. If air resistance is negligible the melon will return to its initial level with a kinetic energy of
100 J.
It takes 40 J to push a large crate 4 m across a floor. The force exerted on the crate is
10N
what is the mass of a ball moving at 4 m/s with a momentum of 48 kg m/s
12 kg
What is the speed of a 6-kg ball with a momentum of 72 kg∙m/s?
12 m/s
what is the mass of a ball moving at 3 m/s with a momentum of 48 kg m/s
16 kg
a 1000 kg truck moving at 10 m/s that brakes to a stop in 5s has an average braking force of
2000 N
A 2-kg mass that weighs 20 N has 40 J of potential energy relative to the ground. What is its height?
2m
What is the speed of a 4-kg ball with a momentum of 12 kg∙m/s?
3 m/s
A music console is pushed 2 m by a force of 20 N. The work done on the console is
40 J.
A bow is drawn so that it has 40 J of potential energy. When the arrow is fired its kinetic energy is ideally
40 j
a 5 kg fish swimming at a speed of 1 m/s swallows an absent-minded 1 kg fish at rest. the speed of the larger fish after lunch is
5/6 m/s
a boxer punches a sheet of paper in midair from rest to a speed of 40 m/s in 0.05 s. if the mass of the paper is 0.01 kg, the force of the punch on the paper is
8.0 N
A 2-kg mass weighs 20 N and is held 4 m above the ground. Its potential energy relative to the ground is
80j
Which has greater kinetic energy: a car traveling at 30 km/h or another car of half the mass traveling at 60 km/h?
The 60-km/h car
An astronaut floating alone in outer space throws a baseball. If the ball moves away at 20 m/s, the astronaut will move in the opposite direction at
a lower speed
which of the following has the largest momentum relative to earth?
a pickup truck speeding along a highway
If a monkey floating in outer space throws his hat away, the hat and the monkey will both move
away from each other, but at different speeds
When you jump from an elevated position you usually bend your knees upon reaching the ground, which makes the time of the contact about 10 times that of a stiff-legged landing. In this way the average force your body experiences is
about 10 times
The force of a falling apple hitting the ground depends upon
all of the above
The massive ram of a pile driver falling from rest strikes a pile with a speed that depends on the
all of the above
a car traveling along the highway brakes to a stop. a greater breaking force is required when the car has
all of the above
a moving object has
all of the above
the amount of potential energy possesed by an elevated object is
all of the above
Bronco's speed increases after he dives from a hovering helicopter. Relative to an observer in the helicopter Bronco's momentum
also increases
When you simultaneously drop a light tennis ball and a heavy bowling ball, they hit the floor
at the same speed
Padded dashboards in cars are safer in an accident than non-padded ones because a person hitting the dash has
both of these
Whether a truck comes to a stop by crashing into a haystack or a brick wall, the impulse is
both the same
which of these two collisions is more damaging; driving into a concrete wall with no "give", or colliding head-on with an identical car moving toward you ar your same speed
both the same
while driving down the highway a mosquito spatters onto your windsheild. which undergoes the greater impulse
both the same
while driving down the highway a mosquito spatters onto your windshield. which undergoes the greater change in momentum during the time of contact.
both the same
while driving down the highway of a mosquito spatters onto your windsheild. which experiences the greater force of impact?
both the same, but with different consenquences
a karate chop is more effective if one's hand
bounces upon impact
When Peter tosses an egg against a sagging sheet, the egg doesn't break due to
neither of these
An open freight car rolls friction free along a horizontal track in a pouring rain that falls vertically. As water accumulates in the car, the car's speed
decreases
When Freddy Frog drops vertically from a tree onto a horizontally-moving skateboard, the speed of the skateboard
decreases
When bullets are fired in a forward direction from a fighter aircraft, the momentum of the aircraft
decreases
Whereas impulse involves the time that a force acts, work involves the
distance that a force acts
a freight train rolls along a track with considerable momentum. if it rolls at the same speed but has twice as much mass, its momentum is
doubled
which has the greater momentum when moving?
either of these depending on speed
The force of air impact upon the sail of a boat is greater if the air
encounters the sail head-on
the unit kilowatt hour is a unit of
energy
When Jean standing on slippery ice catches her leaping dog Daisy, the momentum of both Jean and Daisy after the catch is
equal to their combined momentum before the catch
the force that accelerates a rocker in outer space is exerted on the rocket by the
exhaust gases
The total momentum of a flock of identical birds could be zero only if the birds are
flying in different directions
When Freddy Frog drops vertically from a tree onto a horizontally-moving skateboard, he doesnt slip off the skateboard because of
friction between his feet and the board
a straw is used for a pea shooteer. when you blow through the straw the speed of the emerging pea will be greater if the straw is
full length
a heavy truck and a small car roll down a hill at the same speed and need to stop in the same amount of time. compared with the force to stop the car, the force needed to stop the truck is
greater
When an apple falls to the ground, momentum is transferred to the ground. The momentum absorbed by the ground is
greater if the apple bounces
Whether a truck comes to a stop by crashing into a brick wall or a haystack, the stopping force is
greater with the brick wall
A clerk can lift containers a vertical distance of 1 m, or roll them up a 2-m-long ramp to the same elevation. With the ramp, the applied force needed is
half as much.
the speed of a bullet fired from a gun will be about the same as the speed of the recoiling gun
if the masses of the bullet and gun are equal
A cannonball fired from a long-barrel cannon will have a greater muzzle velocity because the cannonball receives a greater
impulse
the change in momentum of an object is equal to the
impulse that acts on it
compared with falling on a wood floor, a wine glass may not break when it falls on a carpeted floor because of
longer time to stop
When a cannon fires a cannonball at a given speed, the smaller recoil speed of the cannon is due to different
masses
An iron ball and wooden ball of the same size are dropped simultaneously from a tower and reach the ground at the same time. The iron ball has a greater
momentum
a heavy truck and a small truck roll down a hill. neglecting friction, at the bottom of the hill the heavy truck has greater
momentum
an object in motion is an object that has
momentum
a fan attached to an ice sail craft stalled on a windless day blows air into the sail that bounces backward upon impact. the boat
moves in the direction of the wind impact force
An object that has kinetic energy must be
moving
According to the impulse-momentum relationship Ft = change in mv, a falling baseball hits a player with a force of F. the t in the equation is the time
of contact of the ball hitting the player
Work is done by gravity on a bowling ball that rolls
on a sloped surface.
If you push for an hour against a stationary wall, you do no work
on the wall
Consider a gun with a pellet that is more massive than the gun. The firing speed is greater for the
recoiling gun
it is correct to say that impulse is equal to
the change in momentum
To catch a fast-moving softball with your bare hand, you extend your hand forward just before the catch and then let the ball ride backward with your hand. Doing this reduces the catching force because the
time of the catch is increased
the distinction between impulse and force involves the
time the force acts
If you push an object twice as far while applying the same force, you do
twice as much work
When you push an object a certain distance while applying twice the force, you do
twice as much work
A 1000-kg car and a 2000-kg car are hoisted the same vertical distance in a service station. Raising the more massive car requires
twice as much work.
An object lifted 10 m gains a certain amount of potential energy. If it is lifted 20 m, its gain in potential energy is
twice as much.
When you ride your scooter you have momentum. When you ride twice as fast you have
twice the momentum
recoil is noticeable if we throw a heavy ball while standing on a skateboard. if instead we go through the throwing motion but hold onto the ball, without friction effects our net recoil will be
zero