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Grade 11Mechanics

two identical spheres A and b of radius r are released simultaneously in a vessel of radius r+ R and coefficient of restitution is 1/ 2 then velo city of a is

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8 Years agoGrade 11
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2 Answers

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ApprovedApproved Tutor Answer1 Year ago

To determine the velocity of sphere A after it is released in a vessel, we need to analyze the situation step by step, considering the properties of the spheres and the effects of the coefficient of restitution. Let's break it down.

Understanding the Scenario

We have two identical spheres, A and B, each with a radius of r. They are released in a vessel that has a radius of r + R. The coefficient of restitution (e) between the spheres and the vessel is given as 1/2. This coefficient is crucial as it defines how much kinetic energy is conserved during the collision.

Key Concepts

  • Coefficient of Restitution: This value indicates the ratio of relative speeds after and before a collision. An e of 1 means a perfectly elastic collision, while e of 0 means a perfectly inelastic collision.
  • Velocity Before Collision: When the spheres are released, they will accelerate due to gravity until they hit the bottom of the vessel.
  • Velocity After Collision: The velocity after the collision will depend on the coefficient of restitution.

Calculating Velocity Before Collision

When the spheres are released, they fall freely under the influence of gravity. The velocity of a sphere just before it hits the bottom can be calculated using the equation of motion:

v = √(2gh)

Here, g is the acceleration due to gravity, and h is the height from which the sphere falls. In this case, the height is the distance from the top of the vessel to the bottom, which is (R + r).

Thus, the velocity just before impact for sphere A is:

v_A = √(2g(R + r))

Velocity After Collision

After the collision with the bottom of the vessel, we need to apply the coefficient of restitution to find the new velocity. The coefficient of restitution is defined as:

e = (relative velocity after collision) / (relative velocity before collision)

Since sphere A is colliding with a stationary surface (the bottom of the vessel), the relative velocity before the collision is simply the velocity of sphere A just before impact, which we calculated as v_A.

After the collision, the velocity of sphere A (v'_A) can be expressed as:

v'_A = -e * v_A

Substituting the value of e (1/2) and v_A:

v'_A = -1/2 * √(2g(R + r))

Final Result

Thus, the velocity of sphere A after it collides with the bottom of the vessel is:

v'_A = -√(g(R + r))/2

This negative sign indicates that the direction of the velocity is now upwards, as the sphere rebounds after hitting the bottom. This analysis shows how the coefficient of restitution affects the outcome of the collision and the subsequent motion of the spheres.

Profile image of Askiitians Tutor Team
ApprovedApproved Tutor Answer1 Year ago

To determine the velocity of sphere A after it is released in a vessel, we need to consider the dynamics of the situation, particularly the effects of gravity and the coefficient of restitution. Let's break this down step by step.

Understanding the Setup

We have two identical spheres, A and B, both with a radius of r, placed in a vessel that has a radius of r + R. The coefficient of restitution (e) between the spheres is given as 1/2. This coefficient measures how much kinetic energy remains after a collision compared to before. An e of 1/2 means that after a collision, the spheres will retain half of their velocity in the direction of the impact.

Initial Conditions

When the spheres are released, they will start to fall under the influence of gravity. Assuming they are dropped from rest, their initial velocity (v₀) is 0. As they fall, they will accelerate due to gravity (g), which is approximately 9.81 m/s² on Earth.

Velocity Before Collision

As the spheres fall, we can calculate their velocity just before they collide with the bottom of the vessel. The distance they fall is equal to the height of the vessel, which is R (the distance from the top of the vessel to the bottom). Using the kinematic equation:

  • v² = u² + 2as

Here, v is the final velocity, u is the initial velocity (0), a is the acceleration due to gravity (g), and s is the distance fallen (R). Plugging in the values:

  • v² = 0 + 2gR
  • v = √(2gR)

Collision Dynamics

When spheres A and B collide, we need to apply the coefficient of restitution to find the velocities after the collision. If we denote the velocity of sphere A just before the collision as v_A and that of sphere B as v_B, we can express the relationship after the collision using the coefficient of restitution:

  • e = (v_B' - v_A') / (v_A - v_B)

Since both spheres are identical and fall from the same height, they will have the same velocity just before the collision, which we calculated as v = √(2gR). Therefore, we can denote this as:

  • v_A = v_B = √(2gR)

Calculating Post-Collision Velocities

After the collision, we can denote the velocities of spheres A and B as v_A' and v_B', respectively. Since they collide elastically (with e = 1/2), we can rearrange the equation:

  • 1/2 = (v_B' - v_A') / (√(2gR) - √(2gR))

However, since they have the same velocity before the collision, we need to consider that they will not bounce off each other but rather continue moving downwards. The coefficient of restitution will affect how they interact if they collide again or if they hit the bottom of the vessel.

Final Velocity of Sphere A

After the collision, sphere A will continue to move downwards. The velocity of sphere A after the first collision will be:

  • v_A' = (1 - e) * v_A = (1 - 1/2) * √(2gR) = 1/2 * √(2gR)

Thus, the final velocity of sphere A after the collision, considering the coefficient of restitution, will be:

  • v_A' = 1/2 * √(2gR)

In summary, the velocity of sphere A after being released and colliding with sphere B in the vessel is 1/2 times the square root of 2gR. This demonstrates how the coefficient of restitution influences the motion of colliding bodies in a gravitational field.