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Physics Question 91 – AP-EAMCET 2025

If the equation for the displacement of a particle executing simple harmonic motion is x=3sin(2π18t+π6) cm, then the distance travelled by the particle in a time of 36 s is (Time 't' is in second)

Identify the amplitude and angular frequency from the given displacement equation to determine the time period of oscillation.

Step 1: Identify SHM Parameters✦ Active

The given equation for the displacement of a particle executing simple harmonic motion is x=3sin(2π18t+π6) cm. This equation is in the standard form x=Asin(ωt+ϕ), where A is the amplitude, ω is the angular frequency, and ϕ is the initial phase.

By comparing the given equation with the standard form, we can identify the amplitude and angular frequency:

A=3 cm
ω=2π18=π9 rad/s
💡 Teacher's Secret Hint

Always ensure the units are consistent. Here, displacement is in cm and time in seconds.

Step 2: Calculate the Time Period○ Expand

The time period (T) of simple harmonic motion is related to the angular frequency (ω) by the formula:

T=2πω

Substitute the value of ω found in Step 1:

T=2ππ9=2π×9π=18 s
💡 Teacher's Secret Hint

The time period represents the time taken for one complete oscillation. Make sure to cancel out common terms like π correctly.

Step 3: Calculate Distance in One Period○ Expand

In one complete time period (T), a particle executing simple harmonic motion travels a distance equal to four times its amplitude (4A). This is because it moves from its equilibrium position to one extreme (A), back to equilibrium (A), to the other extreme (A), and back to equilibrium (A).

Using the amplitude A=3 cm:

Distance in one period=4A=4×3 cm=12 cm
💡 Teacher's Secret Hint

Remember that displacement is a vector quantity (can be positive or negative), while distance is a scalar quantity and is always positive. For SHM, distance is always 4A for a full cycle.

Step 4: Calculate Total Distance Travelled○ Expand

The total time for which the particle travels is given as ttotal=36 s. We need to find out how many full time periods occur within this total time.

Number of periods=ttotalT=36 s18 s=2

Since the particle completes 2 full time periods, the total distance travelled will be the number of periods multiplied by the distance travelled in one period.

Total distance=2×(Distance in one period)=2×12 cm=24 cm
💡 Teacher's Secret Hint

This method works perfectly for integer multiples of the time period. If the total time were not an integer multiple of T, you would need to consider the phase and position at the start and end of the remaining fraction of a period.

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