2012 #2 Free Response Question - AP Physics C: Mechanics - Exam Solution

What is the primary physical principle being investigated in the experiment described?

• Conservation of momentum

• Conservation of mechanical energy

• Newton's Second Law

• Work-energy theorem

Why is it important to consider the calculations for gravitational potential energy and translational kinetic energy (Part C) when designing the experiment, even before performing it?

• To determine the experimental errors in advance.

• To ensure the experiment is fun and engaging.

• To know how to calculate the quantities for which the experiment is designed.

• To select the most expensive equipment for accurate results.

Which of the following pieces of equipment would be essential for setting up an experiment to investigate the conservation of mechanical energy using an inclined track and a cart, as described by Billy?

• Lightweight low-friction pulley

• String

• Track

• Photogates

In Billy's proposed experiment using an inclined track, which of the following measurements is NOT directly required to calculate the change in gravitational potential energy of the cart?

• Initial height of the cart

• Final height of the cart

• Mass of the cart and objects

• Time taken for the cart to travel a certain distance

What is the initial gravitational potential energy of an object of mass 'm_o' dropped from a height 'h_i' when the horizontal zero line is set at the ground?

• PE_gi = m_o * g * h_i

• PE_gi = 0

• PE_gi = 1/2 * m_o * v_i^2

• PE_gi = m_o * g * h_f

What is the final gravitational potential energy of an object of mass 'm_o' dropped to the ground from a height 'h_i' when the horizontal zero line is set at the ground?

• PE_gf = m_o * g * h_i

• PE_gf = 0

• PE_gf = 1/2 * m_o * v_f^2

• PE_gf = m_o * g * h_f

An object of mass 'm_o' is dropped from rest and takes time 'Δt' to hit the ground. What is the expression for its final kinetic energy just before impact, assuming acceleration due to gravity is 'g'?

• KE_f = 1/2 * m_o * (g * Δt)^2

• KE_f = m_o * g * h_i

• KE_f = 2 * m_o * Δd^2 / Δt^2

• KE_f = 0

In an experiment involving a dropped object, if calculations show that the total mechanical energy decreased, and assuming no mathematical errors, what is a reasonable physical explanation for this result?

• The object was accidentally given an initial upward velocity.

• The horizontal zero line was incorrectly set.

• Nonconservative forces like air friction converted mechanical energy to heat and sound.

• The acceleration due to gravity was miscalculated.