Physics

No (this would violate the law of conservation of energy)

A batter bunts a pitched baseball, blocking the ball without swinging. Can the baseball deliver more KINETIC ENERGY to the bat and batter than the ball carries initially?

Yes (by bouncing back adding another vector the ball can have more momentum than it did initially)

A batter bunts a pitched baseball, blocking the ball without swinging. Can the baseball deliver more momentum to the bat and batter than the ball carries initially?

No (if one object is at rest and another is moving there is an initial momentum greater than zero, so the total momentum after collision would also have to be greater than zero)

If two objects collide and one is initially at rest is it possible for both to be at rest after the collision?

Yes (if all of object A's momentum is transferred to object B)

If two objects collide and one is initially at rest is it possible for only one to be at rest after the collision?

head on collision with objects with the same momentum in opposite directions (transferred to heat energy)

In perfectly inelastic collisions between two objects, there are events in which all of the original kinetic energy is transformed to forms other than kinetic. Give an example of such an event.

No (the clay still imparts all of its momentum against the wall but the size of the wall and its connection to the earth causes there to not be an observable force)

A ball of clay of mass M is thrown with the speed V against a brick wall. The clay sticks to the wall and stops. Is the principle of conservation of momentum violated in this example?

C

A skater is standing still on a frictionless ice rink. Her friends throw her a frisbee. In which of the following cases is the largest momentum transferred to the skater?
a) The skater catches the frisbee and holds onto it
b)the skater catches the frisbee and drops it vertically downward
c) The skater catches the frisbee, holds onto it momentarily and throws it back to her friends

As water is forced out of the holes of the arm, the arm imparts a horizontal impulse to the water, the water then exerts an equal and opposite impulse on the spray arm causing it to rotate in the opposite direction of the spray

In a dish washer water at high pressure is forced out of small holes on the spray arm. Use conservation of momentum to explain why the arms rotate, directing water to all dishes.

No (it would not be elastic because KE is lost in some form, usually heat)

If two vehicles collide, they usually do not stick together. Does this mean the collision is elastic?

All momentum is added together

If two vehicles collide, they usually do not stick together. Explain why a head on head collision is more dangerous.

holding momentum constant

Your PE teacher throws you a tennis ball at a certain velocity, and you catch it. You are now given the following choice: The teacher can throw you a medicine ball with the same velocity, the same momentum, or the same kinetic energy as the tennis ball. Which option would you choose in order to make the easiest catch, and why?

MV (bullet has small mass and a high velocity, the gun has a much larger mass so a smaller velocity)

A sharpshooter fires a rifle while standing with the butt of the gun against his shoulder. If the forward momentum of the bullet is the same as the backward momentum of the gun, why isn't it dangerous to be hit by the gun as by the bullet?

it decreases the force of impact by increasing the amount of time over which the impact occurs

An air bag inflates when a collision occurs, protecting a passenger from serious injury. Why does the airbag soften the blow. Discuss the physics involved?

the follow through keeps the club in contact with the ball as long as possible maximizing impulse causing a greater change in momentum

In golf, novice players are often advised to be sure to follow through with their swing. Why does this make the ball travel a longer distance?

(momentum= Force(time)) by minimizing time and adding the same force you get a lesser momentum that is necessary for a shorter shot

In golf, novice players are often advised to be sure to follow through with their swing. If a shot is taken near the green, very little follow through is required. Why?

the speed must decrease because momentum remains the same while the mass increases

An open box slides across a frictionless, icy surface of a frozen lake. What happens to the speed of the box as water from a rain shower falls vertically downward into the box? Explain.

No (impulse depends on force*time so with a large time interval a large change in momentum can change without a larger net force)

Does a larger net force exerted on an object always produce a larger change in momentum of the object, compared to a smaller net force? Explain.

the right shoulder (the outside of the curve)

In a race like the indianapolis 500, a driver circles the track counterclockwise and feels his head pulled toward one shoulder. To relieve his neck muscles from having to hold his head erect, the driver fastens strap to one wall of the car and the other to his helmet. Which shoulder does his head tend to lean toward?

tension in the neck muscles must produce centripetal acceleration

In a race like the indianapolis 500, a driver circles the track counterclockwise and feels his head pulled toward one shoulder. To relieve his neck muscles from having to hold his head erect, the driver fastens strap to one wall of the car and the other to his helmet. What force or forces produce the centripetal acceleration when there is no strap?

tension in the strap must produce centripetal acceleration (this allows the neck muscles to remain loose)

In a race like the indianapolis 500, a driver circles the track counterclockwise and feels his head pulled toward one shoulder. To relieve his neck muscles from having to hold his head erect, the driver fastens strap to one wall of the car and the other to his helmet. What force or forces produce the centripetal acceleration when there is a strap?

No (astronauts are weightless in orbit because they are in free fall. Actually, being in orbit is only possible because of the Earth's gravity. Without it, a spaceship would fly off into space in a straight line. The Moon, for example, is much farther awa

If someone told you that astronauts are weightless in Earth's orbit because they are beyond the force of gravity, would you accept the statement? Explain.

The speedometer will be inaccurate ( the speedometer measures the number of tire revolutions per second, so its readings will be too low

If a car's wheels are replaced with wheels of greater diameter, will the reading of the speedometer change?

Your bathroom scale is unaffected (because you, the earth, and the scale are all in free fall in the sun's gravitational field)

At night you are further away from the sun than during the day. What is more, the force exerted by the sun on you downward into earth at night and upward into the sky during the day. If you had a sensitive enough scale would you appear to weigh more at night than during the day?

C (the total acceleration here is centripetal acceleration) straight up

A pendulum consists of a small object called a bob hanging from a light cord of fixed length, with the top end of the cord fixed. The bob moves without friction, swinging equally as high on both sides. It moves from its turning point A through point B and reaches max speed at point C. At which point does the bob have nonzero radial acceleration? what is the direction of its total acceleration at this point?

A (the speed at A is zero where the bob is reversing direction. The total acceleration here is tangential acceleration) to the right and downward perpendicular to the cord

A pendulum consists of a small object called a bob hanging from a light cord of fixed length, with the top end of the cord fixed. The bob moves without friction, swinging equally as high on both sides. It moves from its turning point A through point B and reaches max speed at point C. At which point does the bob have nonzero tangential acceleration and zero radial acceleration? what is the direction of its total acceleration at this point?

B (the total acceleration here is to the right and pointing in a direction somewhere between the tangential and radial directions, depending on their relative magnitudes)

A pendulum consists of a small object called a bob hanging from a light cord of fixed length, with the top end of the cord fixed. The bob moves without friction, swinging equally as high on both sides. It moves from its turning point A through point B and reaches max speed at point C. At what point does the bob have both nonzero radial and tangential acceleration? what is the direction of its total acceleration at this point?

Earth's equatorial radius being greater than its polar radius is in fact centripetal acceleration applied to the earth itself

because of Earth's rotation about its axis, you weigh slightly less at the equator than at the poles. Explain.

If the rotational speed is adjusted so that the normal force is equal in magnitude to her weight on earth, she will not be able to distinguish between the artificial gravity and earth's gravity

It has been suggested that rotating cylinders about 10 miles long and 5 miles in diameter be placed in space for colonies. The purpose of their rotation is to simulate gravity for the inhabitants. Explain the concept behind the proposal.

circular motion

Describe the path of a moving object in the event that the object's acceleration is constant in magnitude at all times and perpendicular to its velocity.

free fall

Describe the path of a moving object in the event that the object's acceleration is constant in magnitude at all times and parallel to its velocity.

The tendency of the water is to move in a straight line path tangent to the circular path followed by the container. (As a result, at the top of the circular path, the water presses against the bottom of the pail, and the normal force exerted by the pail

A pail of water can be whirled in a vertical circular path such that no water is spilled. Why does the water remain in the pail, even when the pail is upside down above your head?

according to Kepler's second law the angular momentum of a planet in the orbit is conserved.
(L = m v r = constant, where 'm' is mass, 'v' is speed and 'r' is the distance of the planet
since, when 'm' is constant, 'v' is inversely proportional to 'r' whi

Use Kepler's second law to convince yourself that earth must move faster in its orbit during the northern hemisphere winter, when it is closest to the sun, than during the summer when it is farthest from the sun.

(Any object that moves such that the direction of its velocity changes has an acceleration.) A car moving in a circular path will always have a centripetal acceleration.

Is it possible for a car to move in a circular path in such a way that it has tangential acceleration but no centripetal acceleration?

The speed changes (the component of force tangential to the path causes a tangential acceleration)

An object executes circular motion with constant speed whenever a net force of constant magnitude acts perpendicular to the velocity. What happens to the speed if the force is not perpendicular to the velocity?

In order for you to remain in equilibrium, your center of gravity must always be over your point of support, the feet. If your heels are against the wall, your center of gravity cannot remain above your feet when you bend forward, so you lose your balance

Why can't you put your heels firmly against a wall and then bend over without falling?

Changing the axis of rotation changes lots of things. In particular, it changes -- or may change -- the distance through which some of the mass moves. Consider a meter stick rotated first about its center of mass and then about its end.

Explain why changing the axis of rotation of an object changes its moment of inertia

No (only if its angular velocity changes)

If you see an object rotating, is there necessarily a net torque acting on it?

NO! It is easy to state "find the torque caused by these forces". But that is a meaningless statement. What is always required -- or meant or implied -- is "find the torque with respect to such-and-such center of rotation that is caused by these forces".

Is it possible to calculate the torque acting on a rigid object without specifying an origin? Is the torque independent of the location of the origin?

The long pole had a large moment of inertia about an axis along the rope. An unbalanced torque will then produce only a small angular acceleration of the performer-pole system, to extend the time available to regain balance

Why does a long pole help a tightrope walker stay balanced?

The angular momentum of the gas cloud is conserved. Thus, the product Iw remains constant. As the cloud shrinks in size, its moment of inertia decreases, so its angular speed w must increase

Stars originate as large bodies of slowly rotating gas. Because of gravity, these clumps of gas slowly decrease in size. What happens to the angular speed of a star as it shrinks?

If you have a wheel on a frictionless surface with a force pushing on the centre this should move the wheel along rather then rotate it. Net force non-zero but net torque is zero.

Give an example in which the net force acting on an object is nonzero, yet the net torque is zero

Now imagine the same wheel but with two forces, both have their direction within the plane of the wheel. One force pushes on the rim of the wheel and is a tangent to the wheel. The other force is on the exact opposite rim of the wheel and is also a tangen

Give an example in which the net torque acting on an object is nonzero, yet the net force is zero

floor rough (a smooth wall can exert a normal force to hold the latter in equilibrium against horizontal motion)

A latter rests inclined against a wall. Would you feel safer climbing up the latter if you were told that the floor was frictionless but the wall was rough or that the wall was frictionless and the floor is rough?