PHYS 2102 C876 Conceptual Physics

Explanation:

If two vans of identical properties collide and move together after the collision, it indicates that they have equal mass. In such a perfectly inelastic collision, the conservation of momentum dictates that the total momentum of the system is equally distributed between the two vans. Since both move together post-collision, the conclusion is that their masses must be equal for the velocities to match as observed.

Correct Answer:

The vans were of equal mass.

Why Other Options Are Wrong:

The van at rest has half the mass of the van that was moving.

This is incorrect because if the masses were unequal, the post-collision velocity of the combined vans would be biased toward the more massive van’s momentum, and they would not move together at a common velocity.

The van that was moving has half the mass of the van that was at rest.

This is incorrect for the same reason; unequal masses prevent the vans from moving together after collision at a single velocity.

The van at rest has double the mass of the van that was moving.

This is incorrect because a significantly heavier van at rest would cause the final combined velocity to be much lower than the initial velocity of the moving van. Only equal masses produce the observed behavior.

Explanation:

When a bar magnet is broken into smaller pieces, each piece forms its own north and south pole. This occurs because the magnetic domains within the material, which are regions of aligned atomic magnetic moments, remain aligned in each fragment. Therefore, every piece becomes a complete magnet with both poles, regardless of how many times it is divided. The phenomenon demonstrates that magnetic monopoles do not exist in isolation; magnetic poles always appear in north-south pairs.

Correct Answer:

Each piece becomes a magnet with a north and south pole

Why Other Options Are Wrong:

The pieces lose their magnetic properties

This is incorrect because breaking a magnet does not destroy its magnetic domains. Each fragment retains the alignment of its domains and therefore continues to act as a magnet with both poles.

Only the ends of the original magnet retain their poles

This is incorrect because all pieces, not just the original ends, form new north and south poles. Magnetic poles are not limited to the ends of the original magnet.

The poles of the original magnet are unchanged

This is incorrect because breaking the magnet creates new poles in each fragment. The original poles are not preserved in isolation; they become distributed across the smaller pieces.

Explanation:

In an inelastic collision, the colliding objects stick together and move with a common velocity after the collision. The principle of conservation of momentum is applied: m₁v₁ = (m₁+m₂)v_f

Substituting the values: (2 × 10) + (5 × 0) = (2 + 5)v_f, which simplifies to 20 = 7 v_f. Solving for v_f gives v_f = 20/7 ≈ 2.86 m/s. The closest option provided is 2 m/s, acknowledging approximation in the choices.

Correct Answer:

2 m/s

Why Other Options Are Wrong:

4 m/s

This is incorrect because it overestimates the final speed. The combined mass after the collision is 7 kg, and using momentum conservation, the correct speed is less than 3 m/s.

6 m/s

This is incorrect because this would imply a much smaller combined mass or much larger initial momentum. The calculation shows that 6 m/s is far above the physically possible outcome.

8 m/s

This is incorrect because it greatly overestimates the final velocity. The momentum of the system cannot produce such a high final speed for the combined mass.

Explanation:

Work is defined as the product of the force applied to an object and the displacement of the object in the direction of the force. Mathematically, this is expressed as W=F×d, where W is work, F is force, and dd is the displacement. This formula captures the concept that work is done only when a force causes movement along its line of action. Other expressions like mass times acceleration or power times distance describe related physical quantities but do not work directly.

Correct Answer:

Work = Force × Distance

Why Other Options Are Wrong:

Work = Mass × Acceleration

This is incorrect because mass times acceleration gives force, not work. Work requires a displacement component in the direction of the force.

Work = Energy × Time

This is incorrect because energy multiplied by time does not represent work. Power is the quantity that relates energy and time, not work.

Work = Power × Distance

This is incorrect because power multiplied by distance is not a standard physical definition of work. Power relates work to time, but distance alone does not produce work without the associated force.

Explanation:

For an ideal gas, the average kinetic energy of the gas molecules depends solely on temperature. According to the kinetic theory of gases, the kinetic energy of individual molecules is directly proportional to the absolute temperature (measured in Kelvin). Pressure, volume, and the number of molecules influence the state of the gas but do not directly determine the average kinetic energy per molecule.

Correct Answer:

temperature

Why Other Options Are Wrong:

pressure

This is incorrect because pressure is related to the force exerted by gas molecules on the container walls, not directly to the average kinetic energy of individual molecules. While pressure is connected to kinetic energy through temperature and volume, it is not the primary determining factor.

the number of gas molecules

This is incorrect because the average kinetic energy per molecule is independent of how many molecules are present. The total energy of the gas increases with the number of molecules, but the average per molecule depends only on temperature.

volume

This is incorrect because volume affects gas pressure and density, but the average kinetic energy of individual molecules is not directly dependent on the volume; it depends on temperature.

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:

Gravitational force is given by Newton’s law of universal gravitation: F=Gm1m2r2, where m₁ is the mass of the Earth and m₂  is the mass of the person. A decrease in Earth’s mass m₁ reduces the gravitational attraction between Earth and the person. Since a person’s weight is the gravitational force acting on them, their weight would decrease proportionally to the decrease in Earth’s mass.

Correct Answer:

A decrease in Earth's mass would decrease gravitational force, leading to decreased weight.

Why Other Options Are Wrong:

A decrease in Earth's mass would increase gravitational force, leading to increased weight.

This is incorrect because gravitational force is directly proportional to mass. Reducing Earth’s mass reduces the force, not increases it.

A decrease in Earth's mass would have no effect on gravitational force or weight.

This is incorrect because a person’s weight depends directly on the mass of Earth. Any decrease in mass decreases the gravitational force and therefore weight.

A decrease in Earth's mass would only affect weight if the distance from the center of the Earth changes.

This is incorrect because while distance affects gravitational force, the mass itself also directly influences the force. A change in mass alone changes weight even if the distance remains constant.

Explanation:

The distance traveled by a freely falling object from rest can be calculated using the equation of motion s = 12gt2, where gg is the acceleration due to gravity (approximately 10 m/s²) and t is the time. Substituting the values: s= 12*10*52= 5 × 25 =125 meters. Therefore, the rock falls a distance of 125 meters in 5 seconds.

Correct Answer:

125m

Why Other Options Are Wrong:

100m

This is incorrect because it underestimates the distance. Using s = 12gt2 with t = 5s and g = 10 m/s², the correct calculation yields 125 meters, not 100 meters.

145m

This is incorrect because it overestimates the distance. The formula shows that the rock falls 125 meters, so 145 meters is too large for a 5-second fall under standard gravity.

200m

This is incorrect because it is significantly higher than the calculated distance. For an object in free fall from rest, 5 seconds under g =10 m/s² cannot result in a 200-meter fall.

Explanation:

Knowing the power consumption of a device and using the formula I = WV, where W is the power in watts and V is the voltage, allows an electrician to calculate the current in amperes. This information is critical for selecting the appropriate wire gauge to safely carry the current without overheating or violating electrical codes. Therefore, the calculation helps in sizing the wire for safe operation.

Correct Answer:

Size the wire

Why Other Options Are Wrong:

Locate the breaker box

This is incorrect because calculating current does not provide the physical location of the breaker box. It is unrelated to the task of wire sizing or electrical layout.

Locate the underground power utility

This is incorrect because current calculations have no effect on locating utility infrastructure. It is purely an electrical design calculation.

Reduce the amount of power used (for energy conservation)

This is incorrect because calculating the current does not change energy consumption. Energy conservation involves behavioral or technological changes, not the calculation of existing current.