Exam 2
If the Moon had twice as much mass and still orbits Earth at the same distance, ocean bulges on Earth would be
***dont worry about this one too much*** larger (know that tides have 2 bulges)
A toy elevator is raised from the ground floor to the second floor in 20 seconds. The power needed using 1000 J of work, is
50 W
Which produces more force: driving into a very massive concrete wall with no "give," or having a head-on collision with an identical car moving toward you at the same speed?
the same
Earth's primary energy source is
the sun
A ball rolling down an incline has its maximum potential energy at
the top (highest point)
Strictly speaking, more fuel is consumed by your car if the air conditioner, headlights, or even a radio is turned on. This statement is
true
Two identical arrows, one with twice the kinetic energy of the other, are fired into a bale of hay. Compared with penetration of the slow arrow, the faster arrow penetrates
twice as far
The work you do when pushing a shopping cart twice as far while applying the same force is
twice as much
A cannon recoils while firing a cannonball. The speed of the cannon's recoil is relatively small because the
cannon has much more mass than the cannonball.
If Earth's radius somehow increased with no change in mass, your weight would
decrease (same mass but further away)
When bullets are fired from an airplane in the forward direction, the momentum of the airplane is
decreased
The ram of a pile driver drops onto the top of an iron beam, driving it partway into the ground. The distance that the beam sinks into the ground depends on the
- kinetic energy of the ram when it first hits the beam. - initial potential energy of the ram. - initial height of the ram.
An outcome of universal gravitation is that
-prediction and discovery of planets. -planets aren't cubes with sharp corners. -its discovery prompted other laws of nature.
A 5-kg shark swimming at 1 m/s swallows an absent-minded 1-kg fish swimming toward it at 4 m/s. The speed of the shark after his meal is
1/6 m/s
About 40 J is required to push a crate 4 m across a floor. If the push is in the same direction as the motion of the crate, the force on the crate is about
10 N
A weight watcher who normally weighs 400 N stands on top of a very tall ladder so she is one Earth radius above Earth's surface. How much is her weight there?
100 N the gravitational force varies as 1/r^2 where r is the distance from the center of the earth at the surface of the earth, she is 1 earth radius from the center at the new height, she is 2 earth radii from the center therefore, her distance from the center of the earth has doubled and her weight will change by a factor of 1/2^2 = 1/4 her new weight is 1/4 of her prior weight 1/4 x 400N = 100N
A machine puts out 100 watts of power for every 1000 watts put into it. The efficiency of the machine is
100/1000 = 10%
A 5000-kg freight car moving at 2 m/s collides with a 10,000-kg freight car at rest. They couple upon collision and move away at
2/3 m/s
The work done in pushing a TV set a distance of 2 m with an average force of 20 N is
40 J
A piece of taffy slams into and sticks to an identical piece of taffy at rest. The momentum of the combined pieces after the collision is the same as before the collision, but this is not true of the kinetic energy, which partly degrades into heat. What percentage of the kinetic energy becomes heat?
50% (remains)
Danny Diver weighs 500 N and steps off a diving board 10 m above the water. Danny hits the water with kinetic energy of
5000 J
The change in momentum that occurs when a 1.0 kg ball traveling at 4.0 m/s strikes a wall and bounces back at 2.0 m/s is
6 kg m/s
A 5000-kg freight car collides with a 10,000-kg freight car at rest. They couple upon collision and move at 2 m/s. What was the initial speed of the 5000-kg car?
6 m/s *** know calculation
A motorcycle moving at 50 km/h skids 10 m with locked brakes. How far will it skid with locked brakes when traveling at 150 km/h?
90 m
If an object is placed exactly halfway between Earth and the Moon, it would fall toward the
Earth
If all people, animals, trains and trucks all over the world began to walk or run towards the east (opposite the direction of Earth's spin), then
Earth would spin a bit slower
How far must one travel to escape Earth's gravitational field?
Forget it; you can not travel far enough
Which of the following has the largest momentum relative to Earth's surface? A) a tightrope walker crossing Niagara Falls B) the Science building on campus C) a mouse running across your room D) a pickup truck speeding along a highway E) a Mack truck parked in a parking lot
a pickup truck speeding along a highway
When properly used, a hydraulic press, like a wheel and axle, is capable of multiplying force input.
a true statement
A feather and a coin dropped in a vacuum fall with equal
accelerations
A hydraulic press, like an inclined plane, is capable of increasing energy.
always false
Rate this statement: No force due to Earth's gravity acts on astronauts inside the orbiting space station.
always false
When a cannon is fired, it recoils as the cannonball is set in motion. The cannon and cannonball ideally acquire equal
but opposite amounts of momentum
A firecracker bursts while freely falling. The combined momentum of its fragments
equals the momentum of the firecracker at the time of burst
The force that accelerates a rocket in outer space is exerted on the rocket by the
exhaust gases
The work you do when pushing a shopping cart twice as far while applying twice the force is
four times as much
Freddy Frog drops vertically from a tree onto a horizontally-moving skateboard. The reason he doesn't slip off the skateboard is due to
friction between his feet and the board
A heavy truck and a small car rolling down a hill at the same speed are forced to stop in the same amount of time. Compared with the force that stops the car, the force needed to stop the truck is
greater
According to Newton, the greater the masses of interacting objects, the
greater the gravitational force between them.
A circus diver drops from a high pole into water far below. When he is halfway down
his kinetic energy and potential energy are equal
As two objects moving toward each other due to gravity get closer, the acceleration of each
increases
Padded dashboards in cars are safer in an accident than non-padded ones because passengers hitting the dashboard encounter
lengthened time of contact.
A 2-kg ball is held 4 m above the ground. Relative to the ground its potential energy is
mgh 80 j
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
A moving object has
momentum, speed, energy, velocity
If the Sun became twice as massive, your attraction to the Sun would double and your weight as measured on Earth would
not change
The most concentrated form of energy is
nuclear energy
The force of Earth's gravity on a capsule in space will lessen as it moves farther away. If the capsule moves to twice its distance, the force toward Earth becomes
one-fourth
Earth is presently accelerating toward the Sun (centripetal acceleration). If the Sun collapsed into a black hole, this acceleration would
remain the same
In comparison with other fundamental forces, the universal gravitational constant G indicates that gravity is
very very weak
