Physics 106 - Midterm Exam

TYPICAL MULTIPLE CHOICE QUESTIONS FROM PAST EXAMS OF HOW THINGS WORK II

Problem 1:

You are watching children play a game of tug-o-war with an old plastic clothesline. The two teams are pulling at opposite ends of the cord and each team is trying to drag the other team into a mud puddle that lies between them. After a few minutes without progress, the team on the right suddenly pulls hard toward the right. The team on the left has anticipated this threat and is able to keep their end of the rope from moving at all. The right end of the rope stretches toward the right and the rope breaks. It took energy to breaking the rope and that energy was provided by

(A) the team on the right.

(B) the team on the left.

(D) both teams.

Problem 2:

While an insulator is nearly perfect at preventing the flow of electric current, a semiconductor will permit some current to flow, even in the dark. This current flow is a consequence of thermal energy. In the semiconductor, thermal energy shifts electrons between level so that

(A) both the valence band and the conduction band become full.

(B) the valence band becomes full, while the conduction band becomes empty.

(D) the valence band has a few empty levels and the conduction band has a few filled levels.

Problem 3:

You were heading forward in your car before coming to a complete stop at a red light. The careless driver of the car behind you fails to stop and his car crashes into your car from behind. You suddenly find your head shifted deep into the elastic cushion of your seat's headrest. During the period when your head is deep in the cushion, the net force on your head is

(A) backward and its acceleration is backward.

(B) forward and its acceleration is forward.

(D) zero and it is not accelerating.

Problem 4:

When you bounce a rubber ball off a concrete wall, the ball rebounds at nearly its original speed. During the bounce, the ball

(A) transfers a great deal of momentum and energy to the wall.

(B) retains essentially all of its momentum but transfers a great deal of energy to the wall.

(D) retains essentially all of its energy but transfers a great deal of momentum to the wall.

Problem 5:

A woman leaps off the high diving board during a swimming competition and does a series of flips and spins in the air. As she plunges toward the water, her

(A) angular velocity is constant.

(B) angular momentum is constant.

(D) velocity is constant.

Problem 6:

Suppose that you remove the batteries from an ordinary flashlight, turn them all around, and reinsert them into the flashlight. The batteries and the flashlight’s wires all make good contacts, so that there is no unexpected break in the flashlight’s circuit. If you now turn the flashlight on, it will

(A) glow about twice as bright as usual, but the bulb will burn out soon.

(B) not emit any light.

(D) glow about half as bright as usual.

Problem 7:

You let a permanent bar magnet align freely with an extremely strongly magnetic field. You then rotate the permanent magnet 180° so that it appears to be pointing the wrong way. If you now let the permanent magnet turn freely it will

(A) rotate 180° because it has been demagnetized and is no longer magnetic.

(B) rotate 180° because permanent magnets can’t be remagnetized.

(D) not rotate because it has been demagnetized and is no longer magnetic.

Problem 8:

You have two boxes. In Box A, there is only an electric field that points northward. In Box B, there is only a magnetic field that points westward. You hold a positive charge motionless in each box and then let it go. (Ignore gravity)

(A) The charge in Box A accelerates northward, while the charge in Box B accelerates westward.

(B) The charge in Box A remains motionless, while the charge in Box B accelerates westward.

(D) The charge in Box A accelerates southward, while the charge in Box B accelerates eastward.

Problem 9:

If you hold a stationary positive charge in your left hand and a stationary north magnetic pole in your right hand, the positive charge would exert

(A) a leftward force on the north magnetic pole.

(B) zero force on the north magnetic pole.

(D) an upward force on the north magnetic pole.

Problem 10:

A needle-sharp lightning rod protects the top of a tall tower. This rod is connected by a wire to the earth far below. When a positively charged cloud passes over the tower, the lightning rod

(A) becomes negatively charged and begins to emit negative charges onto passing air particles which help to neutralize the cloud.

(B) becomes negatively charged and repels any lightning strikes so that they hit far away from the tower.

(D) becomes positively charged and repels any lightning strikes so that they hit far away from the tower.

Problem 11:

A positively charged dust particle will stick to an electrically neutral wall because the dust particle will

(A) charge the wall by causing negative charge to be created at the surface of the wall so that the wall and dust attract.

(B) induce an electric current in the wall, making the wall magnetic so that it attracts the dust particle magnetically.

(C) charge the wall by transferring part of its positive charge to the wall so that the wall and dust attract one another.

(D) polarize the wall, shifting the wall’s negative charges toward the dust and the wall’s positive charges away from the dust.

Problem 12:

Moment of inertia is the measure of an object’s rotational inertia. If you wanted to figure out which of two round, symmetric objects has the largest moment of inertia, you should

(A) spin each object in your hand and then drop it to the floor. The one that falls fastest while spinning has the larger moment of inertia.

(B) lift each object and see which one takes the most force to lift upward at constant velocity.

(D) spin each object in your hand and then drop it to the floor. The one that falls slowest while spinning has the larger moment of inertia.

Problem 13:

A permanent magnet sticks motionlessly to the steel front of your refrigerator because the permanent magnet

(A) shifts the electrons and protons in the steel slightly apart, so that a magnetic polarization occurs. The protons have north magnetic poles and the electrons have south magnetic poles.

(B) causes currents to flow in the steel, making the steel magnetic so that it attracts the poles of the permanent magnet.

(D) attracts isolated magnetic poles (also known as monopoles) in the steel toward the surface of the steel, where they bind strongly to the poles of the permanent magnet.

Problem 14:

The secondary coil of a transformer normally winds in one direction around and around the magnetic core. Instead of going all the way around the core, it would be easier for the wire to go half way around the core and then turn around and head back toward its starting point. It could do this many times, creating a zigzag pattern that never actually goes all the way around the core. Such a secondary wire would produce

(A) only half as large a voltage rise as a normal secondary coil.

(B) only a quarter as large a voltage rise as a normal secondary coil.

(D) zero net voltage rise in any current passing through it.

Problem 15:

The lamp on your desk has a short circuit. A fragment of metal is connecting the two wires at the point where the bulb screws into the socket. Because of this short circuit, the bulb glows

(A) normally, but the current in the lamp’s power cord is smaller than usual.

(B) dimly or not at all, but the current in the lamp’s power cord is larger than usual.

(D) more brightly than normal and is likely to burn out.

Problem 16:

The cord of your desk lamp has two wires inside it. It needs two wires because

(A) the power company provides both electric and magnetic power. One wire carries electric power and the other wire carries magnetic power.

(B) one wire carries current to the lamp and the other wire carries current back to the power company.

(D) north and south magnetic poles cannot be separated from one another. The north and south poles must travel together on the two wires.

Problem 17:

If you want to send lots of electric power to a distant consumer and not waste very much of that power, you should use

(A) a very small current of very high voltage charges.

(B) a very small current of very low voltage charges.

(D) a very large current of very low voltage charges.

Problem 18:

Suppose you have two identical-looking sticks, each with exactly the same total mass. In one stick, most of the mass is located at its ends. In the other stick, most of the mass is located at the middle. If you grip both sticks at the middle and exert equal torques on them with your wrists,

(A) the sticks will undergo equal accelerations because they have equal masses.

(B) the stick with its mass near its ends will undergo more angular acceleration.

(D) the sticks will undergo equal accelerations because they have equal moments of inertia.

Problem 19:

You jump off of a diving board into a swimming pool. As you fall toward the water, your velocity

(A) increases, but your acceleration remains constant

(B) increases because your acceleration increases

(D) remains constant because your acceleration is constant

Problem 20:

When it moves slowly on a calm lake, a canoe will coast almost forever at constant velocity. Suppose that two canoes are both coasting northward at constant velocity (no one is paddling) when the rear canoe bumps into the canoe in front of it. There is a loud “thump” sound. Despite the collision, the total

(A) velocity of the two canoes remains unchanged.

(B) kinetic energy of the two canoes remains unchanged.

(D) thermal energy of the two canoes remains unchanged.

Problem 21:

A battery

(A) creates negative charge.

(B) creates positive charge.

(D) pumps positive charge from its negative terminal to its positive terminal.

Problem 22:

A toy top spins for a long time on its point. If you made the point sharper, the top would spin longer because

(A) the force the top exerts on the floor becomes smaller.

(B) the parts of the sharper point travel less far against the force of sliding friction.

(D) the support force that the floor exerts on the top becomes larger.

Problem 23:

Copper is a nonmagnetic metal. When you move the north pole of a bar magnet toward a sheet of copper,

(A) current flows through the copper and repels the approaching north pole.

(B) nothing happens to the copper.

(D) current flows through the copper and attracts the approaching north pole.

Problem 24:

There are no permanent magnets made out of pure aluminum metal because aluminum

(A) does not have enough mass to overcome the inertia of permanent magnetism.

(B) is a soft magnetic material and quickly demagnetizes when you remove it from any external magnetic fields.

(D) has no internal magnetic structure at all.

Problem 25:

A current loses energy as it flows through a wire. Because of this loss of energy, the current experiences a

(A) voltage rise as it passes through the wire and a magnetic field therefore pushes the current forward.

(B) voltage rise as it passes through the wire and an electric field therefore pushes the current forward.

(D) voltage drop as it passes through the wire and an electric field therefore pushes the current forward.