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3. An astronaut lands on an alien planet. He places a pendulum (L = 0.200 m) on the surface and sets it in simple harmonic motion, as shown in this graph.

Answer the following questions:
a. What is the period and frequency of the pendulum’s motion?
b. How many seconds out of phase with the displacements shown would graphs of the velocity and acceleration be?
c. What is the acceleration due to gravity on the surface of the planet in m/s2? Determine the number of g-forces.

2 Answers

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Final answer:

a. The period of the pendulum's motion is 0.5 seconds and the frequency is 2 Hz. b. The graphs of velocity and acceleration would be in phase with the displacement graph. c. The acceleration due to gravity on the surface of the planet is approximately 39.478 m/s², which corresponds to 4.03 g-forces.

Step-by-step explanation:

a. The period of the pendulum's motion can be determined by identifying the time it takes for one complete oscillation. From the graph, we can observe that it takes approximately 0.5 seconds to complete one cycle. Therefore, the period of the pendulum's motion is 0.5 seconds. The frequency can be calculated by taking the reciprocal of the period, which gives us a frequency of 2 Hz.

b. The displacements, velocity, and acceleration of a pendulum in simple harmonic motion can be represented by sine and cosine functions. The phase difference between the displacements, velocity, and acceleration graphs depends on where they start in their respective cycles. Since the pendulum is set at a specific phase in simple harmonic motion, the graphs of velocity and acceleration would be in phase with the displacement graph, meaning there would be no time difference.

c. The acceleration due to gravity on the surface of the planet can be determined using the formula for the period of a simple pendulum: T = 2π√(L/g), where T is the period of the pendulum, L is the length of the pendulum, and g is the acceleration due to gravity. Rearranging the formula, we can solve for g: g = 4π²(L/T)². Substituting the given values of L = 0.2 m and T = 0.5 s, we calculate g to be approximately 39.478 m/s². To determine the number of g-forces, we divide this value by the acceleration due to gravity on Earth (9.8 m/s²): 39.478 m/s² ÷ 9.8 m/s² = 4.03 g-forces.

User Geoff Lanotte
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a). We could read off the period if we had the graph.
The frequency is 1/period.

b). The velocity is the first derivative of the displacement,
so it should lag the displacement by 90° .

The acceleration is the derivative of the velocity,
so that puts it 180° behind the displacement.

c). If we could see the graph, then, knowing the pendulum's
length and the period of its swing, we could calculate the
acceleration of gravity on the planet at which he is at.

The number of 'G-forces' is

9.8 m/s² / (acceleration of gravity where he is at) .

The number is a ratio ... without units.
User Sheralee
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8.5k points