Energy of Simple Harmonic Oscillators

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AP Physics 1 › Energy of Simple Harmonic Oscillators

Questions 1 - 10
1

A block on a spring executes SHM on a level surface. When the block is at equilibrium, its kinetic energy is $20,\text{J}$ and its spring potential energy is $0,\text{J}$. At maximum displacement it is momentarily at rest. What is the spring potential energy at maximum displacement?

$10,\text{J}$

Less than $20,\text{J}$ because energy is lost whenever velocity is zero.

$0,\text{J}$

$20,\text{J}$

Explanation

This problem tests energy conservation in simple harmonic oscillators at extreme positions. In SHM on a frictionless surface, total mechanical energy remains constant throughout the motion. At equilibrium, the block has maximum speed with 20 J of kinetic energy and zero spring potential energy, establishing total energy as 20 J. At maximum displacement where the block is momentarily at rest, all kinetic energy transforms into spring potential energy, so the spring stores all 20 J. Choice D incorrectly suggests energy is lost when velocity is zero, but energy simply changes form rather than disappearing. When solving SHM problems, identify total energy at any point and apply conservation to find energies at other positions.

2

A cart attached to a spring oscillates on a frictionless track in SHM. The equilibrium position is where the spring is unstretched. At the turning points, the cart’s kinetic energy is $0$ and spring potential energy is maximum. At equilibrium, kinetic energy is maximum and potential energy is minimum. Total mechanical energy is constant. The cart is at $x=+A/\sqrt{2}$.

At $x=+A/\sqrt{2}$, which statement about energy is correct?

Potential energy is zero because the cart is moving.

Total mechanical energy is greater than at $x=0$.

Kinetic energy equals spring potential energy.

Kinetic energy is zero because the cart is far from equilibrium.

Explanation

This question tests energy statements at a specific position in simple harmonic motion for a cart-spring system. Total mechanical energy E is constant, exchanging between K and U. At x = A/√2, U = E/2 and K = E/2, as $(x/A)^2$ = 1/2. Thus, kinetic equals potential energy there. Distractor C incorrectly suggests total E is greater than at x=0, but conservation keeps it constant. Calculate the position's $(x/A)^2$ fraction to determine energy equality or ratios in SHM problems.

3

A cart on a spring oscillates in SHM on a level, frictionless track. The equilibrium position is at $x=0$. At $x=\pm A$, the cart stops briefly so kinetic energy is $0$ and spring potential energy is maximum; at $x=0$, kinetic energy is maximum and potential energy is minimum. Mechanical energy is conserved. The cart is at position $x=0$ moving to the right.

Immediately after passing through equilibrium, which statement is correct?

Kinetic energy begins decreasing while potential energy begins increasing.

Kinetic energy remains maximum until the cart reaches the turning point.

Total mechanical energy increases because the cart is still speeding up.

Potential energy is zero everywhere because equilibrium is at $x=0$.

Explanation

This question assesses energy changes immediately after equilibrium in simple harmonic motion for a cart-spring system. In frictionless SHM, total energy is conserved, but K and U exchange as the cart oscillates. After passing equilibrium moving away, K decreases as speed slows, while U increases as the spring stretches or compresses. This continues until the turning point where K=0 and U maximum. Distractor B wrongly claims K stays maximum until the turning point, ignoring the continuous energy transfer. A transferable approach is to consider the direction of motion and position to predict whether K is increasing or decreasing in SHM.

4

A mass–spring oscillator moves without damping. When the mass passes the equilibrium position, its kinetic energy is $6,\text{J}$ and the spring potential energy is $0,\text{J}$. At a turning point the mass is instantaneously at rest. Which statement is correct at the turning point?

Total energy is less than $6,\text{J}$ because the spring has stopped doing work.

Kinetic energy is $0,\text{J}$.

Kinetic energy is $6,\text{J}$.

Total energy is $0,\text{J}$ because both energies are zero there.

Explanation

This problem tests understanding of energy states in simple harmonic oscillators at turning points. In undamped SHM, total mechanical energy remains constant as kinetic and potential energies continuously interchange. At equilibrium, the mass has 6 J of kinetic energy and zero spring potential energy. At a turning point, the mass is instantaneously at rest, meaning velocity and kinetic energy are both zero. All 6 J of total energy is stored as spring potential energy at this position. Choice C incorrectly claims total energy is zero when both energies are zero, not recognizing that potential energy is maximum when kinetic energy is zero. When analyzing SHM at turning points, remember that zero velocity means zero kinetic energy, not zero total energy.

5

A cart on a frictionless track is attached to a spring and oscillates in SHM. At equilibrium, its kinetic energy is $K_\text{max}=14,\text{J}$ and its spring potential energy is $0,\text{J}$. At maximum displacement, the cart is momentarily at rest. Which energy comparison is correct?

At maximum displacement, $K = U$ because energy is shared equally there.

At maximum displacement, $K > U$ because the cart has moved farthest.

At maximum displacement, $U > K$.

At maximum displacement, total energy is smaller than $14,\text{J}$ because the cart stops.

Explanation

This question examines energy distribution in simple harmonic oscillators at different positions. In frictionless SHM, total mechanical energy (14 J) remains constant while kinetic and potential energies exchange. At equilibrium, all 14 J is kinetic energy (K = 14 J, U = 0 J). At maximum displacement where the cart is momentarily at rest, all energy converts to spring potential energy (K = 0 J, U = 14 J), making U > K at this position. Choice A incorrectly claims kinetic energy is greater at maximum displacement, when actually the cart is at rest there. To analyze SHM energy comparisons, identify where speed is maximum (equilibrium) versus zero (turning points).

6

A mass attached to a spring oscillates without friction. At equilibrium position $x=0$, the spring is unstretched and the mass has maximum speed, so kinetic energy is maximum and spring potential energy is minimum. At maximum displacement, the speed is zero and spring potential energy is maximum. Total mechanical energy stays constant. When the mass is at equilibrium, which energy statement is correct?

Kinetic energy is maximum and potential energy is minimum.

Kinetic energy is zero because the displacement is zero.

Potential energy is maximum because the spring force is greatest at equilibrium.

Total mechanical energy is increasing because the mass speeds up through equilibrium.

Explanation

This question assesses energy distribution at equilibrium in simple harmonic oscillators. In frictionless SHM, total mechanical energy stays constant, comprising kinetic and potential components that interchange. At equilibrium (x=0), the spring is unstretched, minimizing potential energy, while the mass's maximum speed maximizes kinetic energy. As it moves outward, kinetic energy decreases and potential increases, peaking at maximum displacement where kinetic is zero. Distractor B incorrectly asserts potential is maximum at equilibrium due to spring force, but force is zero there, and potential is actually minimum. A key strategy is to use conservation of energy to predict that maximum kinetic occurs where potential is minimum, and vice versa.

7

A mass–spring system oscillates in SHM with no friction. At the equilibrium position, the kinetic energy is $K_\text{eq}=5,\text{J}$ and the spring potential energy is $0,\text{J}$. At a turning point, the mass is at rest. Which statement is true at the turning point?

The spring potential energy is $5,\text{J}$.

The total mechanical energy decreases at the turning point due to the spring force.

The kinetic energy is $5,\text{J}$ because acceleration is zero there.

The total mechanical energy is $0,\text{J}$ because the speed is zero.

Explanation

This question examines energy conservation in simple harmonic oscillators at different positions. In frictionless SHM, total mechanical energy remains constant as energy continuously transforms between kinetic and potential forms. At equilibrium, the system has 5 J of kinetic energy and zero spring potential energy, establishing total energy as 5 J. At the turning point where the mass is at rest, all kinetic energy converts to spring potential energy, so the spring stores all 5 J. Choice C incorrectly claims total energy is zero when speed is zero, confusing kinetic energy with total energy. To solve SHM energy problems, recognize that total energy equals the sum of kinetic and potential energies at any instant.

8

A mass on a spring undergoes SHM. At equilibrium, the kinetic energy is $9,\text{J}$ and the spring potential energy is $0,\text{J}$. At maximum displacement, the mass is instantaneously at rest. What is the total mechanical energy at maximum displacement?

Less than $9,\text{J}$ because energy is lost at each turning point.

$18,\text{J}$

$9,\text{J}$

$0,\text{J}$

Explanation

This problem tests understanding of energy conservation in simple harmonic oscillators. In undamped SHM, total mechanical energy remains constant as kinetic and potential energies continuously exchange. At equilibrium, the system has 9 J of kinetic energy and zero spring potential energy, establishing total mechanical energy as 9 J. This total energy remains constant throughout the motion, including at maximum displacement where all energy is potential. Choice D incorrectly suggests energy is lost at turning points, but in SHM without damping, energy is conserved. When solving SHM problems, recognize that total energy can be calculated at any convenient point and remains the same everywhere.

9

A mass on a spring oscillates about equilibrium with negligible friction. At equilibrium, the mass moves fastest, so kinetic energy is greatest and spring potential energy is least. At maximum displacement, the mass stops, so kinetic energy is zero and spring potential energy is greatest. Total mechanical energy remains constant. As the mass moves from equilibrium toward a turning point, which statement is correct about $K$ and $U$?

$K$ increases while $U$ decreases because the spring pulls harder.

Total mechanical energy decreases as the mass approaches the turning point.

Both $K$ and $U$ increase because the mass is moving and the spring is stretching.

$K$ decreases while $U$ increases.

Explanation

This question evaluates energy changes during motion in simple harmonic oscillators. In SHM with negligible friction, total mechanical energy remains constant as kinetic energy converts to potential and back. From equilibrium to a turning point, the increasing displacement raises potential energy, while decreasing speed lowers kinetic energy. At the turning point, all energy is potential, with kinetic at zero. Choice C is a distractor, wrongly suggesting both increase, but they cannot both rise since total energy is fixed. A transferable approach is to analyze energy trends based on position and velocity changes along the path of motion.

10

A mass-spring oscillator moves in SHM with no friction. At equilibrium, the oscillator has $K=9,\text{J}$ and $U=0,\text{J}$. At maximum displacement from equilibrium, the speed is zero. Which comparison is correct at maximum displacement?

Kinetic energy is larger than potential energy because the mass moved farther.

Total energy is less than $9,\text{J}$ because the mass stops at the turning point.

Potential energy is $9,\text{J}$ and kinetic energy is $0,\text{J}$.

Kinetic energy equals potential energy because energy is shared equally at the ends.

Explanation

This problem involves energy conservation in simple harmonic oscillators. For frictionless SHM, total mechanical energy remains constant at K + U = 9 J (from equilibrium values). At maximum displacement, the mass has zero speed, which means kinetic energy K = 0 J. By energy conservation, all 9 J must be stored as potential energy in the spring, so U = 9 J. Choice A incorrectly claims kinetic energy is larger at maximum displacement, when actually kinetic energy is zero there because the mass is momentarily stationary. The strategy is to recognize that at turning points (maximum displacement), all energy is potential since velocity equals zero.

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