Mastering Physics Quiz 3
The crew of a cargo plane wishes to drop a crate of supplies on a target below. To hit the target, when should the crew drop the crate? Ignore air resistance.
Before the plane is directly over the target
When Dr. Hewitt releases the two projectiles, which one hits the ground first?
Both balls hit the ground at the same time
Why do the two objects hit the table at the relative times that they do?
Gravity pulls the same amount on each ball, and they each drop the same distance.
Predict how the vertical component of the velocity will change with time after the projectile is fired.
It first decreases to zero and then increases in the opposite direction.
Is it easier for a circus performer to balance a long rod held vertically with people hanging off the other end, or the same long rod without the people at the other end, and why?
It is easier for the performer to balance a long rod held vertically with people at the other end because the rotational inertia is greater.
Is it easier to balance a long rod with a mass attached to it when the mass is closer to your hand or when the mass is farther away?
It is easier when the mass is farther from your hand.
Predict how the horizontal component of the velocity will change with time after the projectile is fired.
It stays constant.
Why does the rotational inertia of the rod with the attached mass closer to your hand compare the way it does with the rotational inertial of the rod with the attached mass farther away?
Rotational inertia depends on whether the mass is farther or closer to the point of rotation. The farther the mass is, the higher the rotational inertia.
Why does the gravity in the Space Shuttle compare with the gravity on Earth the way it does?
The Space Shuttle and the surface of the Earth are about the same distance from the center of the Earth.
Why do the astronauts in the Space Shuttle float around?
The Space Shuttle is in free fall, so the shuttle and the astronauts inside it are continuously falling toward the Earth. They thus experience apparent weightlessness.
How does the gravity in the Space Shuttle compare with the gravity on Earth's surface?
The gravity in the Space Shuttle is approximately equal to the gravity on the surface of the Earth
How does the rotational inertia of the rod with the mass toward the bottom compare with the rotational inertia of the mass toward the top?
The rotational inertia of the rod with the mass closer to the top is greater than the rotational inertia of the rod with the mass closer to the bottom.
When Dr. Hewitt cuts the broom right through the center of gravity, how do the weights of the two sides of the broom compare?
The shorter side, where the bristles of the broom are, has a greater weight than the handle
How does the torque due to the weight of one side of the broom exerted around the balance point compare with the torque exerted by the weight of the other side of the broom around the balance point?
The torque due to the weight of the shorter side (the bristles of the broom) is equal in magnitude to the torque due to the weight of the longer side, and opposite in direction.
Where is the center of gravity of the broom that Dr. Hewitt holds up?
at the balance point
Consider Earth and the Moon. As you should now realize, the gravitational force that Earth exerts on the Moon is equal and opposite to that which the Moon exerts on Earth. Therefore, according to Newton's second law of motion __________.
the Moon has a larger acceleration than Earth, because it has a smaller mass
