PHYS 2102 C876 Conceptual Physics

Explanation:

The principle of conservation of momentum states that in the absence of external forces, the total momentum of a system remains constant. When the ice-skater catches the ball, the momentum of the ball is transferred to the skater, causing the skater to move. However, the total momentum of the ice-skater and ball system remains the same before and after the catch. Momentum is redistributed within the system, but no external forces act to change the system’s total momentum.

Correct Answer:

The momentum of the system remains constant before and after the catch.

Why Other Options Are Wrong:

The momentum of the system increases as the ball is caught.

This is incorrect because momentum cannot increase without an external force. The system’s total momentum is conserved, not increased.

The momentum of the system decreases as the ice-skater moves backward.

This is incorrect because the system is isolated; momentum does not decrease. The skater’s backward movement is simply a redistribution of momentum between the skater and the ball.

The momentum of the system is transferred entirely to the ice-skater.

This is incorrect because the momentum is shared between the ice-skater and the ball; the total system momentum remains unchanged, not entirely concentrated in the skater.

Explanation:

Hydrogen nuclei (protons) naturally repel each other due to their positive charges. The force preventing them from coming together is the repulsive electrical (electrostatic) force. To achieve nuclear fusion, the protons must be moving fast enough to overcome this repulsion so that the strong nuclear force, which binds nucleons together, can take over and hold them together in a fused nucleus.

Correct Answer:

repulsive electrical

Why Other Options Are Wrong:

strong nuclear

This is incorrect because the strong nuclear force is what actually binds nucleons together once they are close enough. It is not the force that needs to be overcome to initiate fusion; rather, it is the attractive force that enables fusion once repulsion is overcome.

strong gravitational

This is incorrect because the gravitational force between protons is negligibly small compared to the electrostatic repulsion. Gravity does not play a significant role in overcoming proton repulsion for fusion at atomic scales.

attractive magnetic

This is incorrect because magnetic forces are irrelevant in overcoming the repulsion between hydrogen nuclei. Fusion depends on electrostatic and nuclear forces, not magnetism.

Explanation:

When a bar magnet is broken, each resulting fragment becomes a smaller magnet with its own north and south poles. This occurs because the magnetic domains within each piece realign so that the dipole structure is preserved. Magnetic monopoles do not exist, so it is impossible for a fragment to contain only a north or south pole. The internal rearrangement ensures that each piece maintains a complete magnetic field with both poles.

Correct Answer:

The magnetic domains realign in each piece to form new poles

Why Other Options Are Wrong:

The magnetic field is concentrated at the ends of the magnet

This is incorrect because while the field is stronger near the ends, this does not explain why each piece develops both poles when broken. The phenomenon is due to domain alignment, not field concentration.

Magnetic monopoles are created when a magnet is broken

This is incorrect because magnetic monopoles have never been observed in normal materials. Breaking a magnet never produces a single isolated north or south pole.

The original poles are transferred to the new pieces

This is incorrect because the poles are not “transferred.” Each fragment forms its own north and south poles based on the alignment of magnetic domains, rather than inheriting the original poles as separate entities.

Explanation:

The temperature change of an object is given by ΔT = Qmc', where Q is the heat added, m is the mass, and c is the specific heat. A smaller mass and lower specific heat result in a larger temperature increase for the same amount of heat. Calculating ΔT for each:

• Water: ΔT=10/(1⋅4.184)≈2.39°C


• Carbon: ΔT=10/(2⋅0.720)≈6.94°C


• Iron: ΔT=10/(5⋅0.451)≈4.44°C


• Copper: ΔT=10/(5⋅0.385)≈5.19°C


• Gold: ΔT=10/(20⋅0.128)≈3.91°C
  
  The largest temperature increase occurs for 2 g of carbon.

Correct Answer:

2 g carbon (graphite)(specific heat= 0.720 J/gC)

Why Other Options Are Wrong:

1 g water (specific heat= 4.184 J/gC)

This is incorrect because water has a very high specific heat, meaning it requires more energy to raise its temperature. Therefore, the temperature increase is smaller compared to substances with lower specific heat.

5 g iron (specific heat= 0.451 J/gC)

This is incorrect because, although iron has a lower specific heat than water, the larger mass reduces the temperature change, making it smaller than carbon’s increase.

5 g copper (specific heat= 0.385 J/gC)

This is incorrect because the larger mass offsets the low specific heat, resulting in a smaller temperature increase than carbon despite copper’s low specific heat.

20 g gold (specific heat= 0.128 J/gC)

This is incorrect because the very large mass of gold significantly reduces the temperature rise, even though it has a low specific heat.

Explanation:

Potential energy is the energy stored in an object due to its position or configuration. Water stored at a height in a reservoir has gravitational potential energy because of its elevated position relative to the base of the dam. This energy can be converted into kinetic energy as the water is released, but while it is stored, it exemplifies high potential energy.

Correct Answer:

water stored in a reservoir behind a dam

Why Other Options Are Wrong:

swinging a baseball bat

This is incorrect because a swinging bat has kinetic energy due to its motion, not stored potential energy. Its energy is active, not stored by position.

water rushing down a waterfall

This is incorrect because once the water is in motion, it has kinetic energy. Potential energy is highest when the water is stored at height before falling, not while it is moving.

Explanation:

In projectile motion, the vertical component of velocity is affected by gravity. As the projectile rises, gravity continuously decelerates the upward motion until the vertical velocity becomes zero at the peak of the trajectory. At this maximum height, the projectile has no vertical motion momentarily, but it still has horizontal velocity. The vertical velocity reaching zero is a direct consequence of the constant downward acceleration due to gravity.

Correct Answer:

The vertical velocity decreases to zero due to gravity.

Why Other Options Are Wrong:

The projectile has stopped moving.

This is incorrect because the projectile continues to move horizontally; only the vertical component of velocity is zero at the maximum height.

The gravitational force is zero at maximum height.

This is incorrect because gravity acts on the projectile throughout the motion, including at the peak. Gravity is responsible for reducing the vertical velocity to zero.

The angle of launch affects the vertical component.

This is incorrect because while the launch angle determines the initial vertical velocity, the vertical component becomes zero at maximum height regardless of the angle, due to gravity acting downward.

Explanation:

Newton’s third law states that for every action, there is an equal and opposite reaction. When a gun is fired, the bullet moves forward due to the force exerted by the expanding gases, and the gun recoils backward with equal and opposite force. This exemplifies action and reaction forces acting on two different objects, which is the essence of Newton’s third law.

Correct Answer:

A gun recoils when shot

Why Other Options Are Wrong:

Unbelted passengers will be thrown forward when a car stops suddenly

This is incorrect because this is an example of inertia (Newton’s first law), not action-reaction. The passengers continue moving forward due to their inertia when the car stops.

The acceleration of an object when a force is applied depends on the mass of an object

This is incorrect because this describes Newton’s second law, F = ma, not the third law of equal and opposite forces.

The weight of an object varies from planet to planet

This is incorrect because this relates to gravitational force differences, not action-reaction forces. Weight variation depends on the local gravitational field, not Newton’s third law.











 

Explanation:

Electric field lines originate from positive charges and terminate at negative charges. If point C is between a positive charge at A and a negative charge at B, the field lines naturally point from the positive charge toward the negative charge. Therefore, the lines will converge toward the negative charge (B). If a third test charge is introduced at C, it will experience a net force in the direction of the field, but field lines themselves do not converge on arbitrary points like C; they converge on negative charges. The correct conceptual understanding is that lines always go from positive to negative

Correct Answer:

The lines will only originate from point A towards point C.

Why Other Options Are Wrong:

The lines will converge towards point C from both A and B

This is incorrect because electric field lines do not converge on neutral test points. Convergence occurs only at negative charges, not at arbitrary locations between charges.

The lines will diverge from point C towards A and B

This is incorrect because field lines do not diverge from intermediate points; they originate from positive charges.

The lines will form a closed loop around point C

This is incorrect because electric field lines never form closed loops. They always start at positive charges and end at negative charges.

Explanation:

Centripetal force is the net force that keeps an object moving in a circular path. It always acts along the radius of the circle and is directed toward the center of the circle. This inward-directed force continuously changes the direction of the object’s velocity, keeping it on a circular trajectory rather than moving off in a straight line.

Correct Answer:

Along the radius of the circle, toward the center

Why Other Options Are Wrong:

Along the radius of the circle, away from the center

This is incorrect because a force directed outward is called centrifugal force in a rotating reference frame, not the real centripetal force that causes circular motion.

Tangent to the circle, in the direction of motion

This is incorrect because a tangential force affects the speed of the object along the circular path, not the direction toward the center. Centripetal force is always radial, not tangential.

Tangent to the circle, opposite to the direction of motion

This is incorrect because, again, a tangential force in the opposite direction would decelerate the object along the path but would not provide the inward pull necessary for circular motion. Centripetal force is always directed toward the center of the circle.