PHYS 2300 BYT1 Physics: Mechanics

Explanation:

The correct answer is "Both A & B." A second-class lever is characterized by having the load positioned between the fulcrum and the effort. Both a wheelbarrow and a nutcracker fit this description: in a wheelbarrow, the wheel acts as the fulcrum, the load is in the middle, and the person applies effort at the handles. In a nutcracker, the hinge is the fulcrum, the nut is the load in the middle, and effort is applied at the handles. This configuration allows a smaller effort to move a larger load efficiently.

Correct Answer:

Both A & B

Why Other Options Are Wrong:

Wheelbarrow

While a wheelbarrow is indeed a second-class lever, selecting only this option ignores the fact that a nutcracker is also a second-class lever, making the single-choice answer incomplete.

Nutcracker

A nutcracker alone is also a second-class lever, but the question asks for all second-class levers among the options. Only selecting this ignores the wheelbarrow, making it incomplete.

Seesaw

This is a Class 1 lever, where the fulcrum is between the effort and the load, so it does not qualify as a second-class lever.

Explanation:

The correct answer is "simple machines." Mechanical advantage measures how effectively a simple machine—such as a lever, pulley, wheel and axle, or inclined plane—can amplify an input force to accomplish work. It quantifies the ratio of output force to input force, reflecting the machine’s ability to make tasks easier. This concept is central to mechanics and engineering, as it allows a smaller force to move larger loads efficiently through the design of simple machines.

Correct Answer:

simple machines

Why Other Options Are Wrong:

electrical circuits

While electrical circuits can transform energy, the concept of mechanical advantage does not apply to them. Mechanical advantage specifically refers to force amplification in mechanical systems, not electrical systems.

thermal energy

Mechanical advantage does not relate to heat or energy transfer in thermal systems. Thermal energy deals with energy due to particle motion, not the ratio of forces in mechanical systems.

chemical reactions

Chemical reactions involve energy changes and transformations, but they do not amplify mechanical force through devices or systems, so mechanical advantage is not relevant in this context.

Explanation:

The correct answer is "Speed is the total distance traveled divided by time, whereas velocity includes direction." Speed is a scalar quantity that measures how fast an object is moving regardless of direction. Velocity, on the other hand, is a vector quantity that specifies both magnitude and direction of motion. This distinction accurately separates the two concepts: speed considers only how much distance is covered over time, while velocity includes the direction of movement, making this the correct choice.

Correct Answer:

Speed is the total distance traveled divided by time, whereas velocity includes direction

Why Other Options Are Wrong:

Speed is a vector quantity, while velocity is a scalar quantity

This is incorrect because it reverses the definitions. Speed is a scalar, not a vector, and velocity is a vector quantity, so this statement misrepresents the fundamental properties of the two.

Velocity can change even if speed remains constant

While this statement is true in physics—for example, in uniform circular motion where speed is constant but direction changes—it does not directly distinguish speed from velocity. It describes a situation rather than defining the two concepts.

Velocity is always greater than speed

This is incorrect because the magnitude of velocity (speed) can never exceed the speed itself; in fact, the magnitude of velocity is equal to speed when direction is constant. The statement is logically false.

Explanation:

To maximize the distance of a baseball hit, the optimal strategy is to strike the ball at an angle that maximizes projectile range, typically around 30–45 degrees relative to the ground. This allows the ball to achieve an ideal combination of vertical and horizontal motion. Contact at this optimal angle, combined with sufficient force and bat speed, ensures that the ball travels the greatest distance according to the principles of projectile motion in physics.

Correct Answer:

ensure the bat makes contact with the ball at an optimal angle

Why Other Options Are Wrong:

strike the ball with minimal force

This is incorrect because minimal force would not provide enough kinetic energy to the ball for maximum distance. Maximizing distance requires sufficient force, not minimal.

swing the bat at a slower speed

This is incorrect because a slower swing reduces the velocity imparted to the ball, decreasing the distance it travels. High bat speed contributes to greater kinetic energy transfer.

hit the ball with a flat trajectory

This is incorrect because a flat trajectory (close to horizontal) would reduce the time the ball stays in the air and limit distance. An optimal angle is necessary to balance height and horizontal range.

Explanation:

Throughout the entire motion—going up, at the top, and coming down—the only vertical acceleration is due to gravity, which acts downward and is conventionally negative if upward is positive. It never becomes zero or positive.

Correct Answer:

Negative, Negative, Negative

Why Other Options Are Wrong:

Negative, Zero, Negative

This is incorrect because the vertical acceleration is not zero at the top; gravity continues to act downward.

Positive, Zero, Negative

This is wrong because the acceleration is never upward (positive) and never zero at the top.

Negative, Zero, Positive

This is incorrect because acceleration is never zero and never changes sign; it remains downward (negative) at all times.

Explanation:

The correct answer is "its vertical velocity is zero." At the peak of its trajectory, the projectile momentarily stops moving vertically, so its vertical component of velocity is zero. However, the acceleration due to gravity remains constant and downward throughout the motion, so the projectile does not stop accelerating. For a vertically thrown projectile, there is no horizontal velocity to consider, so only the vertical velocity becomes zero at the top.

Correct Answer:

its vertical velocity is zero

Why Other Options Are Wrong:

it stops accelerating

This is incorrect because acceleration due to gravity acts downward continuously, even at the top of the path.

its acceleration changes

This is wrong because gravitational acceleration is constant in magnitude and direction near Earth’s surface.

its horizontal velocity changes

This is incorrect because for a purely vertical throw, there is no horizontal component of velocity; thus, it does not change.

Explanation:

Pressure is defined as the amount of force applied per unit area. It quantifies how concentrated a force is over a surface and is a fundamental concept in fluid mechanics and physics. The correct mathematical representation of pressure is Pressure = Force ÷ Area, which means that for a given force, the pressure increases as the area over which the force is applied decreases. Pressure is not simply a force in different units, nor is it the product of force and area or force and distance.

Correct Answer:

force divided by the area over which the force acts

Why Other Options Are Wrong:

same as force but expressed in different units

This is incorrect because pressure and force are distinct physical quantities. Pressure depends on both the force and the area over which it is applied, not just a unit conversion of force.

force times the area over which the force acts

This is incorrect because multiplying force by area gives a different physical quantity, not pressure. Pressure decreases as the area increases for the same force, which contradicts this formula.

force times the distance over which the force acts

This is incorrect because multiplying force by distance calculates work, not pressure. Pressure is independent of distance and only relates to force and area.

Explanation:

The correct answer is "T=rF." Torque is defined as the rotational equivalent of force, representing the tendency of a force to cause an object to rotate about an axis. The magnitude of torque is calculated as the product of the force applied and the perpendicular distance (moment arm) from the axis of rotation to the line of action of the force. Therefore, the formula T = rF correctly expresses this relationship, where T is torque, r is the moment arm, and F is the applied force.

Correct Answer:

T=rF

Why Other Options Are Wrong:

T=F/r

This is incorrect because torque is not calculated by dividing force by distance. Doing so would incorrectly reduce the effect of force on rotation instead of scaling it proportionally with the moment arm.

T=ma

This formula represents Newton’s second law for linear motion, where force equals mass times acceleration, not torque. It does not relate to rotational effects.

T=Iw

This formula is used to describe rotational inertia and angular momentum (torque in relation to rotational acceleration) but is not the general definition of torque. It applies only in specific dynamics contexts, not the basic torque formula.

Explanation:

For an object in free fall, the distance fallen under constant gravitational acceleration can be calculated using the formula:

d = ½ g t²

where g = 9.8 m/s² (approximate value of gravitational acceleration) and t is the time in seconds. Substituting t = 20 s:

d = ½ × 9.8 × (20)² = 0.5 × 9.8 × 400 = 4.9 × 400 = 1960 m

Rounding to the closest option gives approximately 2000 meters.

Correct Answer:

2000 meters

Why Other Options Are Wrong:

500 meters

This is incorrect because it significantly underestimates the distance fallen over 20 seconds of free fall under gravity.

4000 meters

This is incorrect because it overestimates the distance. Doubling the correct calculation leads to 4000 m, which is not accurate.

25 meters

This is incorrect because it represents a very small fraction of the distance an object would fall over 20 seconds.