**AP Physics 1 Question 247: Answer and Explanation**

### Test Information

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**Question: 247**

**2.** A block attached to an ideal spring undergoes simple harmonic motion about its equilibrium position (x = 0) with amplitude A. What fraction of the total energy is in the form of kinetic energy when the block is at position *x* = *A* ?

- A.
- B.
- C.
- D.

**Correct Answer:** D

**Explanation:**

**D**

By Conservation of Mechanical Energy, *K* + *U _{S}* is a constant for the motion of the block. At the endpoints of the oscillation region, the block's displacement,

*x*, is equal to ±

*A*. Since

*K*= 0 here, all the energy is in the form of potential energy of the spring,

*kA*

^{2}. Because

*kA*

^{2}gives the total energy at these positions, it also gives the total energy at any other position.

Using the equation *U _{S}*(

*x*) =

*kx*

^{2}, find that, at

*x*=

*A*.

Therefore,