phst test 2
Two billiard balls of the same mass roll straight towards each other. the first has a velocity of +5 m/s and the second has a velocity of -3m/s. after colliding, the second ball has a velocity of
+5 m/s
how much work is done on a crate as it slides 10 m across the floor at a constant velocity of 2 m/s?
0 J
Two 1 kg billiard balls roll towards each other moving speed 10 m/s. what is the combined momentum of the two balls?
0 kg m/s
On a balanced see saw, a boy 3x as heavy as his partners sits
1/3 the distance from the fulcrum
on a balanced see saw, a boy 3x as heavy as his partner sits
1/3 the distance from the fulcrum
50 W of power can do how much work in 2 seconds?
100 J
how much work is done pushing a crate with 36 N of force over a distance a 3 m?
108 J
A car moves 4x as fast as another identical car. compared to the slower car, the faster car has
16 times the KE
A 5-kg shark swimming at the sped of 1 m/s swallows an absent-minded 1-oh fish swimming towards at 1 m/s. The speed of the shark after this meal is
2/3 m/s
if the efficiency of a machine is 30%, how much input power is necessary to get 60 Watts of output power?
200 Watts
A 1000 kg car moving at 10 m/s brakes to a stop in 5 s. The average braking force is
2000 N
to tighten a bolt, you push with a force of 40 N at the end of a wrench handle that is 1/8 m from the axis of the bolts. assuming that you wish perpendicular to the wrench handle, the torque you are exerting is
5 Nm
a diver who weighs 500 N steps off a diving board that is 10 m above the water. the diver hits the water with kinetic energy of
5000 J
A cars engine is 20% efficient. when cruising, the car encounters an average retarding force of 1000 N. if the energy content of gasoline is 40 megajoules per liter, how many kilometers per liter does the car get?
8
A 2-kg mass is held 4 m above the ground. what is the approximate potential energy of the mass with respect to the ground?
80 J
A car moving at 30 mk/hr skids 10 m with locked brakes. how far will the car skid with locked breaks if it were traveling at 90 km/hr?
90m
the bead has minimum kinetic energy at point
A
If a piece of sheet metal is cut into the shape shown, its center gravity is at
D
When you are in the passenger seat of a car turning left, you feel pressed against the right side door. the door's push on you is related to ___ and your push on the door is related to ___.
Newtons 1 and Newtons 3 law
when you jump from an elevated position you usually bend your knees upon reaching the ground. by doing this, you make the time of the impact about 10x as great as for a stiff-legged landing. in this way the average force your body experience is:
about 1/10 as great.
a hydraulic press, like a simple level, is capable of multiplying energy input
always false
A washing machine is in the spin cycle. the net force on the clothes in the tub is ____, and the net force on the water that escapes through the holes in the tub is ____/
direct toward the center of the tub; zero
Your pet hamster sits on a spinning record player. if the angular speed of the record player doubles and he moves to a point twice as far from the center, then his linear speed?
doubles
two pool balls each moving at 2 m/s, roll toward each other and collide. suppose after bouncing apart, each moves at 4 m/s. this collision violates conservation of
energy
which requires the most amount of work by the brakes of a car?
equal amount for either
For a very tall skyscraper, the center of the mass is?
is slightly higher than the center of gravity
an SUV will tip over more easily than a sedan built on the same chassis because
its center of mass is higher
if the polar icecaps melted, the resulting water would spread over the entire earth. this new mass distribution would tend to make the length of a day
longer
Stand a meter skick on the end and let go and it rotates to the floor. if you attach a heavy weight to its upper end and repeat, the falling time will be
more
an astronaut, floating alone in outer space, throws a baseball. if the ball floats away at a speed of 20 m/s, the astronaut will,
move in the opposite direction, but at a lower speed
An object that has kinetic energy must be
moving.
a heavy truck and light truck roll down a hill. neglecting friction, at the bottom of the hill, the light truck will have greater
none of these
a large heavy truck and a small baby carriage roll down a hill. neglecting friction at the bottom of the hill, the baby carriage will have a greater
none of these
Suppose you are a the center of a large freely-rotating horizontal turntable in a carnival funhouse. as you crawl toward the edge, the angular momentum of you and the turntable
remains the same, but the RPMs decrease
A hula hoop has more angular momentum when it is
rolling down a hill with an angular speed of 30 RPM
Centrifugal forces are an apparent reality to observers in a reference frame that is
rotating
in autumn, leaves fall from the trees down to the earth. this new mass distribution would tend make the length of the day
shorter
a ring, a disk, and a solid sphere begin rolling down the hill together. the one to reach the bottom first is the
sphere
It is correct to say that impulse is equals to
the change in momentum
is is correct to say that impulse is equal to
the change in momentum
a light truck and a heavy truck move with the same momentum. more work is required to stop the
the lighter truck
a running back carrying the football is about to be stopped in his tracks by one of two defenders; a 180 lb safety or a 320 lb lineman. all 3 players have the same momentum. which defender will most likely inflict the most pain on the running back and why?
the safety because he has greater kinetic energy
if you push an object twice as far, while applying half the force, you do
the same amount of work
A carnvial has a Ferris wheel where the seats are located halfway between the center and outside rim. Compared with a Ferris Wheel with seats on are on the outside rim, your angular speed while riding on this ferris wheel would be
the same and your tangential speed less
If you do half the usual work on an object in twice the usual time, your power output is
twice the usual power output
In which situation does a long, thin, round metal pole have greater angular momentum?
twirling like a baton about the center of its length with an angular speed of 2 RPM