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Grade 12th passMechanics

Two pendulum bobs A and B are hung side by side in contact with one another at rest, each supported by a thread 2m long. A has a mass of 0.2kg and B has a mass 0.08kg. Bob A is then pulled to one side with its thread tight until it is 0.1m higher.Then it is released so that it collides with B.After collision, B gains 0.15m of height. Calculate the speed of A before impact

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4 Years agoGrade 12th pass
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ApprovedApproved Tutor Answer1 Year ago

To find the speed of pendulum bob A just before it collides with bob B, we can use the principles of energy conservation. When bob A is raised to a height of 0.1 meters, it gains potential energy, which will be converted into kinetic energy as it swings down. Let's break this down step by step.

Understanding Potential Energy

Potential energy (PE) is given by the formula:

PE = mgh

where:

  • m = mass of the object (in kg)
  • g = acceleration due to gravity (approximately 9.81 m/s²)
  • h = height above the reference point (in meters)

Calculating the Potential Energy of Bob A

For bob A, which has a mass of 0.2 kg and is raised to a height of 0.1 m, the potential energy can be calculated as follows:

PE_A = m_A * g * h_A

Substituting the values:

PE_A = 0.2 kg * 9.81 m/s² * 0.1 m

PE_A = 0.1962 J

Conservation of Energy

When bob A is released, this potential energy is converted into kinetic energy (KE) just before the impact with bob B. The kinetic energy is given by the formula:

KE = 0.5 * m * v²

At the moment before the collision, all the potential energy has been converted into kinetic energy:

PE_A = KE_A

Thus:

0.1962 J = 0.5 * m_A * v_A²

Solving for the Speed of Bob A

Now we can rearrange the equation to solve for the speed (v_A) of bob A:

0.1962 J = 0.5 * 0.2 kg * v_A²

Multiplying both sides by 2 to eliminate the fraction:

0.3924 J = 0.2 kg * v_A²

Next, divide both sides by 0.2 kg:

v_A² = 0.3924 J / 0.2 kg

v_A² = 1.962 m²/s²

Finally, take the square root to find v_A:

v_A = √(1.962 m²/s²)

v_A ≈ 1.4 m/s

Final Thoughts

Thus, the speed of bob A just before it collides with bob B is approximately 1.4 m/s. This analysis illustrates how energy conservation principles can be applied to solve problems involving pendulums and collisions. If you have any further questions or need clarification on any part of this process, feel free to ask!