PHYS 2102 C876 Conceptual Physics

Explanation:

According to the theory of relativity, as an object approaches the speed of light, its relativistic mass increases. This occurs because the energy required to continue accelerating the object increases dramatically as its velocity nears the speed of light, effectively increasing the inertial resistance. This principle prevents any object with mass from reaching or exceeding the speed of light.

Correct Answer:

The mass increases.

Why Other Options Are Wrong:

The mass decreases.

This is incorrect because relativistic effects cause the mass to increase with speed, not decrease. Decreasing mass would violate the principles of energy-momentum conservation in relativity.

The mass remains constant.

This is incorrect because in classical mechanics mass is constant, but relativity introduces velocity-dependent mass. As speed approaches light speed, relativistic mass increases.

The mass becomes zero.

This is incorrect because only massless particles, like photons, have zero rest mass. Objects with mass cannot become massless according to the theory of relativity.

Explanation:

When an object rests on a horizontal surface without accelerating, it is in a state of equilibrium. The desk exerts an upward normal force that balances the downward gravitational force (weight) acting on the computer. This ensures that the net force on the computer is zero, preventing it from accelerating downward. According to Newton’s third law, the force exerted by the desk must equal the weight of the computer to maintain this balance.

Correct Answer:

The desk applies a force equal to the weight to prevent the computer from accelerating downward.

Why Other Options Are Wrong:

The weight of the computer is less than the force exerted by the desk.

This is incorrect because if the desk exerted a greater force than the weight, the computer would accelerate upward, which does not occur in a stationary scenario.

The desk exerts a force that is always greater than the weight of any object.

This is incorrect because the normal force adjusts to match the weight of the object. It is not inherently greater for all objects.

The computer's weight is irrelevant to the force exerted by the desk.

This is incorrect because the normal force directly depends on the computer’s weight. The two forces must balance to maintain equilibrium.

Explanation:

The tension in the rope of a tire swing depends on the total weight acting on it, which includes both the child and the swing, as well as the gravitational acceleration. The rope must support the combined weight to keep the system in equilibrium when stationary and must also handle additional forces when the swing is in motion. If the swing moves, the tension increases due to the centripetal force at the lowest point of the swing. Therefore, an accurate calculation of rope tension considers the total mass, gravitational force, and motion-related forces.

Correct Answer:

The weight of the child and the swing, along with gravitational acceleration.

Why Other Options Are Wrong:

Only the weight of the child is considered.

This is incorrect because the rope must also support the weight of the swing itself. Ignoring the swing’s weight underestimates the tension in the rope and can lead to unsafe conditions.

The speed of the swing and the height of the tree branch.

This is incorrect because while speed can influence tension dynamically, the height of the branch alone does not directly determine the rope tension. The primary contributors are the weights and gravitational acceleration.

The angle of the swing and the material of the rope.

This is incorrect because the angle affects the direction of forces but not the magnitude of tension directly in a basic calculation, and the material of the rope determines strength but is not part of the tension calculation itself

Explanation:

The period of a simple pendulum is given by T=2πLg, where L is the length of the pendulum and gg is the acceleration due to gravity. A longer pendulum results in a longer period, causing the clock to run slow. To correct a slow-running clock, the period must be decreased, which is achieved by shortening the pendulum’s string. Shortening reduces the time for each swing, allowing the clock to run at the correct pace.

Correct Answer:

Shorten the string to decrease the period

Why Other Options Are Wrong:

Shorten the string to increase the period

This is incorrect because shortening the pendulum reduces the period, not increases it. Increasing the period would make the clock run slower, worsening the problem.

Lengthen the string to decrease the period

This is incorrect because lengthening the pendulum increases the period, which would make the clock run even slower.

Lengthen the string to increase the period

This is incorrect because although lengthening does increase the period, this adjustment would exacerbate the slow-running issue rather than correct it.

Explanation:

The current produced by an electrical device can be calculated using the formula I = PV, where I is current, P is power, and V is voltage. Substituting the given values: I = 62040 =15.5A. This calculation shows that the solar panel produces 15.5 amperes of current when operating at the specified power and voltage.

Correct Answer:

15.5 A

Why Other Options Are Wrong:

12.5 A

This is incorrect because it underestimates the current. Using the formula I = P/V, the correct current is higher.

18.5 A

This is incorrect because it overestimates the current. The calculated current using the given power and voltage is 15.5 A.

20.5 A

This is incorrect because it significantly overestimates the current. The correct calculation yields 15.5 A, not 20.5 A.

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:

Power is defined as the rate at which work is done or energy is transferred. Mathematically, it is expressed as P=Wt, where P is power, W is work, and tt is the time taken. This relationship indicates that for the same amount of work, completing it in less time requires more power, and conversely, performing work slowly requires less power. Therefore, power quantifies how quickly work is accomplished rather than the total work itself.

Correct Answer:

Power is the rate at which work is accomplished.

Why Other Options Are Wrong:

Power is the ability to do work.

This is incorrect because the ability to do work refers to energy, not power. Power measures the rate of doing work, not the capacity to do it.

Power determines the strength of work completed.

This is incorrect because power does not define the magnitude of work but rather how quickly that work is performed.

Power mediates the effect of energy on work.

This is incorrect because power is not a mediator; it is a measure of work done over time. Energy and work are related directly, and power describes the temporal rate of that work.

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:

In static equilibrium, the vertical component of the tension in the rope must balance the weight of the trapeze artist. Let T be the tension, and θ = 30° the angle with the vertical. The vertical component is T cos⁡ θ = W, so T = wcos⁡θ =800cos⁡θ. Since cos ⁡30°≈ 0.866, T ≈ 8000.866 ≈ 924 N. Therefore, the tension in the rope is 924 N.

Correct Answer:

924 N

Why Other Options Are Wrong:

400 N

This is incorrect because it underestimates the tension. It does not account for the angle and the need for the vertical component to support the weight.

196 N

This is incorrect because it significantly underestimates the tension. The vertical component of such a small tension would not balance the 800 N weight.

461 N

This is incorrect because it only accounts for roughly half of the necessary tension to balance the vertical weight component.

786 N

This is incorrect because it underestimates the required tension. The correct calculation using T = Wcos⁡θ gives 924 N.