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?

$0,\text{J}$

$20,\text{J}$

$10,\text{J}$

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

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?

Kinetic energy equals spring potential energy.

Potential energy is zero because the cart is moving.

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

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 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.

4

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 the cart has moved farthest.

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

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).

5

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 zero because the displacement is zero.

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

Kinetic energy is maximum and potential energy is minimum.

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

6

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.

$9,\text{J}$

$18,\text{J}$

$0,\text{J}$

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.

7

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.

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.

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

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.

8

A mass attached to a spring oscillates in SHM on a frictionless surface. At equilibrium position, the measured kinetic energy is $2,\text{J}$ and the spring potential energy is $0,\text{J}$. At maximum displacement, the mass is momentarily at rest. Which statement about energies at maximum displacement is correct?

Total mechanical energy changes with time, so $K+U$ is not constant.

Kinetic energy is maximum at maximum displacement, so $K=2,\text{J}$ there.

Potential energy equals $2,\text{J}$ and kinetic energy equals $0,\text{J}$.

Some energy is lost at the turning point, so $U<2,\text{J}$.

Explanation

This problem tests understanding of energy conservation in simple harmonic oscillators. In frictionless SHM, total mechanical energy remains constant throughout oscillation. At equilibrium, K = 2 J and U = 0 J, giving a total of 2 J. At maximum displacement where the mass is momentarily at rest, velocity equals zero, so kinetic energy K = 0 J. By conservation of energy, all 2 J must be stored as spring potential energy, making U = 2 J. Choice A incorrectly claims kinetic energy is maximum at maximum displacement, when it's actually zero there since the mass stops momentarily. Remember that in SHM, energy continuously exchanges between kinetic and potential forms while maintaining a constant total.

9

A cart on a spring undergoes SHM without damping. When it passes through equilibrium, $K=7,\text{J}$ and $U=0,\text{J}$. When it reaches a turning point, its speed is zero. What must be true about the potential energy at the turning point?

It is $0,\text{J}$ because equilibrium is where potential energy is stored.

It is $7,\text{J}$ because all energy is potential energy when speed is zero.

It is less than $7,\text{J}$ because some energy is lost at each turning point.

It is greater than $7,\text{J}$ because potential energy increases over time.

Explanation

This question examines energy conservation in simple harmonic oscillators. In undamped SHM, mechanical energy is conserved, so the total K + U remains constant at 7 J (from equilibrium). At a turning point where speed equals zero, kinetic energy must be 0 J (since K = ½mv²). Therefore, all 7 J of mechanical energy exists as spring potential energy at the turning point. Choice C incorrectly suggests energy is lost at turning points, but energy only transforms between forms without being destroyed in conservative systems. To solve SHM energy problems, identify total energy from any known state and apply conservation to find energy distribution at other positions.

10

A block on a horizontal spring oscillates without friction. At the equilibrium position, the block’s kinetic energy is $K_0$ and its spring potential energy is $0$. Later, when the block is at maximum displacement, it is momentarily at rest. Which statement about the energies at maximum displacement is correct?

The spring potential energy is $K_0$ because all the mechanical energy is stored in the spring.

The total mechanical energy increases above $K_0$ because the spring does work on the block.

The kinetic energy is $K_0$ because speed is greatest at maximum displacement.

The total mechanical energy is less than $K_0$ because energy is lost at the turning point.

Explanation

This problem tests understanding of energy conservation in simple harmonic oscillators. In SHM without friction, total mechanical energy remains constant throughout the motion. At equilibrium, all energy is kinetic (K₀), while at maximum displacement, the block is momentarily at rest so all energy converts to spring potential energy. Since total energy is conserved, the spring potential energy at maximum displacement must equal K₀. Choice A incorrectly states the block has maximum speed at maximum displacement, when actually speed is zero there. When solving SHM energy problems, remember that total mechanical energy stays constant, with continuous exchange between kinetic and potential forms.

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