Ch 5 - Gravitation and Circular Motion
Which of the following point towards the center of the circle in uniform circular motion?
Acceleration.
Velocity, acceleration, net force.
Velocity, acceleration.
Velocity, net force.
Acceleration, net force.
E
Engines, including car engines, are rated in horsepower. What is horsepower?
The force needed to start the engine.
The force needed to keep the engine running at a steady rate.
The energy the engine needs to obtain from gasoline or some other source.
The rate at which the engine can do work.
The amount of work the engine can perform.
D - horsepower is a measure of power, which is the rate at which you perform work
A small boat coasts at constant speed under a bridge. A heavy sack of sand is dropped from the bridge onto the boat. The speed of the boat
increases.
decreases.
does not change.
Without knowing the mass of the boat and the sand, we can’t tell.
B - Momentum is unchanged, mass increased so speed must decrease
Which pulls harder gravitationally, the Earth on the Moon, or the Moon on the Earth? Which accelerates more?
The Earth on the Moon; the Earth.
The Earth on the Moon; the Moon.
The Moon on the Earth; the Earth.
The Moon on the Earth; the Moon.
Both the same; the Earth.
Both the same; the Moon.
F - Newton's third law says the force are the same, second law says the acceleration must be greater for smaller mass
When the speed of your car is doubled, by what factor does its kinetic energy increase?
sqrt(2).
2.
4.
8.
C - KE = (1/2)mv^2. Since v is squared, doubling it quadruples KE
Two identical billiard balls traveling at the same speed have a head-on collision and rebound. If the balls had twice the mass, but maintained the same size and speed, how would the rebound be different?
At a higher speed.
At slower speed.
No difference.
C - doubling mass doubles both the initial and final momenta, so speed can stay the same
A space shuttle in orbit around the Earth carries its payload with its mechanical arm. Suddenly, the arm malfunctions and releases the payload. What will happen to the payload?
It will fall straight down and hit the Earth.
It will follow a curved path and eventually hit the Earth.
It will remain in the same orbit with the shuttle.
It will drift out into deep space.
it is freely falling but it has a high tangential velocity.
C - it maintains its speed (newton's first law), which was already enough to supply centripetal motion and stay in orbit
A satellite in circular orbit around the Earth moves at constant speed. This orbit is maintained by the force of gravity between the Earth and the satellite, yet no work is done on the satellite. How is this possible?
No work is done if there is no contact between objects.
No work is done because there is no gravity in space.
No work is done if the direction of motion is perpendicular to the force.
No work is done if objects move in a circle.
C
An astronaut is a short distance away from her space station without a tether rope. She has a large wrench. What should she do with the wrench to move toward the space station?
Throw it directly away from the space station.
Throw it directly toward the space station.
Throw it toward the station without letting go of it.
Throw it parallel to the direction of the station’s orbit.
Throw it opposite to the direction of the station’s orbit.
A - to conserve momentum, she will move towards the station
A child whirls a ball in a vertical circle. Assuming the speed of the ball is constant (an approximation), when would the tension in the cord connected to the ball be greatest?
At the top of the circle.
At the bottom of the circle.
A little after the bottom of the circle when the ball is climbing.
A little before the bottom of the circle when the ball is descending quickly.
Nowhere; the cord is stretched the same amount at all points.
B - Tension needs to counteract gravity and supply centripetal force
A bowling ball is dropped from a height h onto the center of a trampoline, which launches the ball back up into the air. How high will the ball rise?
Significantly less than h.
More than h. The exact amount depends on the mass of the ball and the springiness of the trampoline.
No more than h—probably a little less.
Cannot tell without knowing the characteristics of the trampoline.
C - Energy is generally conserved (but in real life never perfectly)
You are lying in bed and want to shut your bedroom door. You have a bouncy “superball” and a blob of clay, both with the same mass. Which one would be more effective to throw at your door to close it?
The superball.
The blob of clay.
Both the same.
Neither will work.
A - Bouncing back means a larger impulse, means a larger force
In the International Space Station which orbits Earth, astronauts experience apparent weightlessness because
the station is so far away from the center of the Earth.
the station is kept in orbit by a centrifugal force that counteracts the Earth’s gravity.
the astronauts and the station are in free fall towards the center of the Earth.
there is no gravity in space.
the station’s high speed nullifies the effects of gravity.
C
Two balls are thrown off a building with the same speed, one straight up and one at a 45° angle. Which statement is true if air resistance can be ignored?
Both hit the ground at the same time.
Both hit the ground with the same speed.
The one thrown at an angle hits the ground with a lower speed.
The one thrown at an angle hits the ground with a higher speed.
Both (a) and (b)
B - Energy is conserved so if they start with the same speed they should end with the same speed (since they both only have KE at the beginning and end). However, their trajectories are different and will require different amounts of time to complete
A small car and a heavy pickup truck are both out of gas. The truck has twice the mass of the car. After you push both the car and the truck for the same amount of time with the same force, what can you say about the momentum and kinetic energy (ke) of the car and the truck? Ignore friction.
They have the same momentum and the same ke.
The car has more momentum and more ke than the truck.
The truck has more momentum and more ke than the car.
They have the same momentum, but the car has more kinetic energy than the truck.
They have the same kinetic energy, but the truck has more momentum than the car.
D - same force and time = same impulse = same momentum imparted. However, larger mass means lower speed and thus lower ke