Midterm 1 Study Guide

When you are struck by a moving object, is it favorable that the object makes contact with you over a short time or over a long time? Explain.

A long time so that the force to your body is reduced.

Which has a greater momentum: a heavy truck at rest or a moving skateboard?

A moving skateboard

How many forces are required for an interaction

A pair of forces

What type of path does a moving object follow in the absence of force?

A straight line path

In terms of impulse and momentum, why do air bags in cars reduce the risk of injury in accidents?

Air bags increase the time of impact and reduce the force on a person during an accident

What does it mean to say something is in mechanical equilibrium?

All of the forces acting on the object cancel out

An apple hanging from a limb has potential energy because of its height. If it falls, what becomes of this energy just before it hits the ground?

All of the potential energy is converted into kinetic energy

Correct your friend who says, "The dragster rounded the curve at a constant velocity of 100 km/h."

An object going around a curve cannot be moving at a constant velocity

If a skater who is spinning pulls her arms in so as to reduce her rotational inertia by half, by how much will her angular momentum change? By how much will her rate of spin increase?

Angular momentum remains the same, while her rate of spin doubles

Why is a black hole invisible?

Because light cannot escape it

The sum of kinetic and potential energies is a constant for satellites in _________ orbit.

Both circular and elliptical orbits

If our Sun shrank in size to become a black hole, but the mass stayed the same, how would Earth's orbit would be affected?

Earth's orbit would not be affected

Which of the following expresses Newton's law of universal gravitation in words and as an equation?

Every body in the universe attracts every other body with a force that, for two bodies, is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. F=G(m1xm2)/d^2

Why do we say that force is a vector quantity?

Force is a vector because it involves two quantities; magnitude and direction

A circularly-moving object requires a centripetal force. What supplies the centripetal force for satellites that orbit the Earth?

Gravitation

When a rifle is fired at a distant target, why isn't the gun barrel aligned so that it points exactly at the target?

Gravity will cause the bullet to veer downward, so the gun should point slightly above the target

Why is kinetic energy a constant for a satellite in a circular orbit but not an elliptical orbit?

In a circular orbit, no work is done by gravity on the satellite

What kind of speed is registered by an automobile speedometer?

Instantaneous speed

When you whirl a can at the end of a string in a circular path, what is the direction of the force you exert on the can?

Inward along the rope, toward the center of rotation

When the speed of a moving car is doubled, how much more kinetic energy does it have?

It has four times the kinetic energy

Why is it advantageous to roll with the punch in boxing?

It increases the amount of time the glove is in contact with you, decreasing the force on your body

If the net force of a sliding block is somehow tripled, what happens to the acceleration?

It triples

What is the difference between linear momentum and angular momentum?

Linear momentum involves straight-line motion; angular momentum involves rotational motion

In which is momentum conserved: an elastic collision or an inelastic collision?

Momentum is conserved during both elastic and inelastic collisions

Can force produce a torque when there in no lever arm?

No, a torque requires both force and a lever arm

In elliptical orbits, Johannes Kepler discovered that the ________ squared was proportional to the radial ____________ cubed.

Period, distance

The gravitational force between two planets is _________ if the masses of both planet are doubled but the distance between them stays the same.

Quadrupled

If all of Earth's inhabitants moved to the equator, how would this affects Earth's rotational inertia? How would it affect the length of a day?

Rotational inertia increases; angular rotation decreases; the length of a day increases

What is rotational inertia, and how is it similar to inertia as studied in earlier chapters?

Rotational inertia is resistance to change in rotational motion, which is similar to ordinary inertia, which is a resistance to change in linear motion

How can gravity be simulated in an orbiting space station?

Rotational motion results in a "fictitious" centrifugal force that behaves like the force of gravity

On a rotating turntable, which of these quantities varies with distance from the center?

Tangential speed

State Newton's second law of motion

The acceleration produced by a net force on an object is proportional to the net force and inversely proportional to the mass of an object

Consider a baseball player batting a ball. What is the action-reaction pair for when the ball is being hit?

The bat hits the ball and the ball hits the bat

Compared with a car moving at some original speed, how much work must the brakes of a car supply to stop a car that is moving twice as fast?

The breaks must do four times as much work when the car is moving twice as fast

Why is centrifugal force in a rotating frame called a "fictitious force"?

The centrifugal force does not actually exist

How does the force of gravity between two bodies change when the distance between them is double?

The force of gravity it one-fourth as much

A stone is thrown upward at an angle. What happens to the horizontal component of its velocity as it rises? As it falls?

The horizontal component remains constant when rising and when it falls

law states: the force decreases as the square of increasing distance, or force increases with the square of decreasing distance.

The inverse square

When the mass of a moving object is doubled with no change in speed, by what factor does its kinetic energy change?

The kinetic energy increases by a factor of 2

How does the MASS of an astronaut change when he or she leaves Earth to visit the International Space Station?

There mass does not change

True or false: In a circular orbit, the kinetic energy of the satellite is constant.

True

The force of gravity between two objects is ________ when their masses are doubled and the distance between them is also doubled.

Unchanged

What is the main difference between speed and velocity?

Velocity is a vector quantity that contains both speed and direction

The ___________ component of velocity for a projectile changes with time.

Vertical

At what part of an elliptical orbit does an Earth satellite have the lowest speed?

When furthest away from earth

At what part of an elliptical orbit does an Earth satellite have the greatest speed?

When nearest to earth

State Newton's third law of motion.

When one object exerts a force on a second object, the second object exerts an equal and opposite force on the first