exam 2 Flashcards
A 60 W incandescent light bulb and a 6 W led both give off the same light. Compare the cost of burning a 60 W incandescent light bulb to the cost of burning a 6 W led light bulb for 24 hours.
The LED is 10 times cheaper because it uses 10 times less energy
A wheel rotates with an angular speed of 3 radians per second and it has a radius of 2 meters. What is the linear speed of a bug located on the outer radius is this wheel?
6 m/s
the power expended doing 100 J of work in 50 s is
2 W
When a twirling ice skater brings her arms inward, her rotational speech
increases
In considering the work energy theorem, the work done on an object by a net force is always
equal to the objects change in kinetic energy
On a rotating turntable, how do tangential speed and rotational speed vary with distance from the center?
tangential speed increases with distance, rotational speed is constant
a 2-kg ball is held 4 m above the ground. relative to the ground its potential energy is
80 J
Two objects have the same mass and radius. One is a hoop and the other is a solid cylinder. If you race the two objects down an incline neglecting air resistance, which do you expect to reach the bottom of the incline first?
the solid cylinder because it has a lower rotational inertia and so it will have the greater acceleration
Freddy Frog drops vertically from a tree onto a horizontally moving skateboard. The skateboard slows. Which of the following are reasons for this?
- the momentum is conserved, so now with the extra mass on the board the velocity will be less
- adding Freddy’s mass increases the force of friction
- Freddy will cause additional air resistance as he adds to the frontal surface area in the direction of motion
tidal friction is causing
the earth to slow its rotation rate very, very gradually
a same-size iron ball and wooden ball are dropped simultaneously from a tower and reach the ground at the same time. The iron ball has a greater
momentum
which of the following is NOT true in regard to centrifugal force?
centrifugal force is a real force that pulls outward on an object that is undergoing circular motion
consider a satellite in an elliptical orbit about earth. which of the following is NOT true?
the speech of the satellite is greatest when it is farther from earth
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
the rotational inertia of an object is greater when most of the mass is located
away from the rotational axis
when the distance between two stars decreases by one-third, the force between them
increases to nine times as much
a ball rolling down an incline has its maximum potential energy at
the top
a stationary 200 kg person is initially holding 50 kg ball while standing on a skateboard. the person throws he ball to the right, and the ball moves with a speed of 12 m/s. the person on the skateboard
moves to the left with a speed of 3 m/s
why do we only see one side of the moon which is the “man in the moon” face of the moon?
we only see one side because tidal effect have slowed is rotation rate until it is already tidally locked in a synchronous orbit
a bicycle that travels four as fast as another when braking to stop will skid
sixteen times as far
which of the following is a unit of work?
joule
a seesaw is balanced with the fulcrum at its midpoint. If a 3 kg weight is placed one meter from the fulcrum on one side, where would you need to place a 6 kg weight on the opposite side in order to balance the seesaw again?
one half meter from the fulcrum
a 2 kg rifle that is suspended by strings fires a .01 kg bullet at 200 m/s. the recoil velocity of the rifle is about
1 m/s
a light aluminum ball and heavy lead ball of the same size roll down an incline. when they are halfway down the incline, they will have the same
none
you exert a 50 N force on one end of a simple lever and move this end of the lever down half a meter. the other end exerts a 100 N force upward and moves an object resting there
one quarter of a meter
In Einsteins theory of gravitation, we understand the gravitational field as
a warping of space time by a massive object
how does the greenhouse effect work? what is the physics?
the sun warms the ground, which causes the ground to radiate in infra-red wavelengths that are strongly absorbed by carbon dioxide and other green house gases, causing the lower atmosphere to warm
what does it mean for a gas to be green house gas?
the gas is in the atmosphere and it strongly absorbs infrared radiation
a 1 kg rock is suspended from the tip of a horizontal meter stick at the 0/cm mark so that the meter stick barely balances like a seesaw when its fulcrum is at the 25/cm mark. from this information, the mass of the meter stich is
1 kg
a simple machine like a pulley can do all of the following except
create energy
a 5000 kg freight car moving at 2 m/s collides with a 10,000 kg freight care at rest. they couple upon collision and move away at
2/3 m/s
a possible way for a black hole to be created in nature is that
a massive star must collapse until the escape velocity at the event horizon becomes so large light cannot escape
if a ping pong ball and a golf ball both move in the same direction with the same amount of kinetic energy, the speed of the ping pong ball must be
more than the golf ball
the famous leaning tower of pisa doesn’t topple over because its center of gravity is
above a place of support
an object that has kinetic energy must be
moving
if you exert a net torque on an object you will find that
the object may speed up or slow down its rotation rate
a firecracker bursts while freely falling. the combined momentum of its fragments
equals the momentum of the firecracker at the time of burst
which of the following are considered greenhouse gases
carbon dioxide and water vapor
the work done in pushing a TV set a distance of 2 m with an average force of 20 N is
40 J
NASA has more than a dozen space probes orbiting the earth keeping tabs on changes in our climate. what have these probes discovered
- they have found that sea level is rising and global temperature is rising
- they have found that artic sea ice is being lost at a rate of 13% each decade
- they have found that carbon dioxide content in the atmosphere is higher that and any time in the last 1 million years
