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A body of mass \(2 \mathrm{~kg}\) moving with a velocity of \(3 \mathrm{~m} / \mathrm{s}\) collides head-on with a body of mass \(1 \mathrm{~kg}\) moving in opposite direction with a velocity of \(4 \mathrm{~m} / \mathrm{s}\). After collision two bodies stick together and moves with a common velocity which in \(\mathrm{m} / \mathrm{s}\) is equal to (a) \(\frac{1}{4}\) (b) \(\frac{1}{3}\) (c) \(\frac{2}{3}\) (d) \(\frac{3}{4}\)

Short Answer

Expert verified
The common velocity is \(\frac{2}{3} \text{ m/s}\) (option c).

Step by step solution

01

Understand the Concept of Conservation of Momentum

In this problem, we apply the principle of conservation of momentum, which states that the total momentum of a closed system before and after a collision is conserved. This means the total momentum of both bodies before collision equals the total momentum after collision.
02

Calculate Initial Momentum

The initial momentum of the system is the sum of the momenta of both bodies. For the first body: momentum is \(2 \text{ kg} \times 3 \text{ m/s} = 6 \text{ kg m/s}\). For the second body, moving in the opposite direction: momentum is \(-1 \text{ kg} \times 4 \text{ m/s} = -4 \text{ kg m/s}\). Thus, the total initial momentum: \(6 - 4 = 2 \text{ kg m/s}\).
03

Write the Equation for Conservation of Momentum

After the collision, the two bodies stick together, and hence the total mass is \(2 + 1 = 3 \text{ kg}\). Let the common velocity be \(v\). The conservation of momentum equation is: \(2 = 3v\).
04

Solve for the Common Velocity

Rearrange the equation to solve for \(v\): \(v = \frac{2}{3} \text{ m/s}\).
05

Choose the Correct Option

The calculated common velocity \(\frac{2}{3} \text{ m/s}\) matches option (c).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Inelastic Collision
In an inelastic collision, two objects collide and become one single entity, sticking together after impact. This is different from an elastic collision where objects bounce off each other without sticking together. Inelastic collisions are fascinating because while momentum is conserved, kinetic energy is not. Some of it gets transferred into other forms of energy like sound, heat or deformation.

To imagine an inelastic collision, consider two cars bumping into each other and moving as one instead of bouncing off. The combined mass is the sum of both vehicles, altering how they move together post-collision. This concept helps us understand various real-world scenarios, especially in safety and crash impact studies.

So, if two masses collide and stick together, as described in our original problem, this is an excellent example of an inelastic collision. The total system's momentum, not energy, remains constant, which is crucial to understanding how they behave following the impact.
Momentum Calculation
Understanding momentum calculation is vital to studying collisions. Momentum is the product of an object's mass and velocity. It's a vector quantity, meaning both magnitude and direction are crucial. In our original exercise, we calculate the momentum of two bodies before they collide.

Here's how we approach it:
  • First, compute the momentum of each object separately. The first body's momentum is given by: \(2 \text{ kg} \times 3 \text{ m/s} = 6 \text{ kg m/s}\).
  • The second object, moving the opposite direction, has its momentum calculated as: \(-1 \text{ kg} \times 4 \text{ m/s} = -4 \text{ kg m/s}\).
  • Sum these values to find the total initial momentum: \(6 - 4 = 2 \text{ kg m/s}\).

Understanding these steps is crucial because they set the foundation for employing the conservation of momentum in predicting outcomes after a collision.
Common Velocity After Collision
The key outcome of an inelastic collision is finding the common velocity of the combined mass. After the collision, both bodies share a resultant velocity, moving together as one unit.

Utilizing the conservation of momentum principle really shines here. Since the total momentum doesn't change, the equation we use before and after the event stays consistent. Given the total initial momentum we've already calculated as \(2 \text{ kg m/s}\), here's how we find the common velocity:
  • After the collision, the combined mass is \(2 + 1 = 3 \text{ kg}\).
  • Let the common velocity be \(v\).
  • The equation for conservation of momentum here is: \(2 = 3v\).

By solving \(v = \frac{2}{3} \text{ m/s}\), we determine the final moving speed of the bodies together. This calculation is vital as it determines how the bodies will continue to move post-collision, offering insights into practical applications like vehicle crash safety and dynamics.

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Most popular questions from this chapter

A small block of mass \(M\) moves with velocity \(5 \mathrm{~ms}^{-1}\) towards an another block of same mass \(M\) placed at a distance of \(2 \mathrm{~m}\) on a rough horizontal surface. Coefficient of friction between the blocks and ground is \(0.25\). Collision between the two blocks is elastic, the separation between the blocks, when both of them come to rest, is \(\left(g=10 \mathrm{~ms}^{-2}\right)\) (a) \(3 \mathrm{~m}\) (b) \(4 \mathrm{~m}\) (c) \(2 \mathrm{~m}\) (d) \(1.5 \mathrm{~m}\)

Which of the following does the centre of mass lie outside the body? (al A pencil (b) A shotput (c) A dice (d) A bangle

A bullet of mass \(20 \mathrm{~g}\) and moving with \(600 \mathrm{~ms}^{-1}\) collides with a block of mass \(4 \mathrm{~kg}\) hanging with the string. What is velocity of bullet when it comes out of block, if block rises to height \(0.2 \mathrm{~m}\) after collision? IUP SEE 2006] (a) \(200 \mathrm{~ms}^{-1}\) (b) \(150 \mathrm{~ms}^{-1}\) (c) \(400 \mathrm{~ms}^{-1}\) (d) \(300 \mathrm{~ms}^{-1}\)

Two blocks of masses \(10 \mathrm{~kg}\) and \(4 \mathrm{~kg}\) are connected by a spring of negligible mass and placed on a frictionless horizontal surface. An impulsive force gives a velocity of \(14 \mathrm{~ms}^{-1}\) to the heavier block in the direction of the lighter block. The velocity of centre of mass of the system at that moment is (a) \(30 \mathrm{~ms}^{-1}\) (b) \(20 \mathrm{~ms}^{-1}\) (c) \(10 \mathrm{~ms}^{-1}\) (d) \(5 \mathrm{~ms}^{-1}\)

Three identical sphere lie at rest along a line on a smooth horizontal surface. The separation between any two adjacent spheres is \(L\). The first sphere is moved with a velocity \(u\) towards the second sphere at time \(t=0 .\) The coefficient of restitution for collision between any two blocks is \(1 / 3\). Then choose the correct statement. [a) The third sphere will start moving at \(t=\frac{5 L}{2 u}\) (b) The thind sphere will start moving at \(t=\frac{4 L}{u}\) (c) The centre of mass of the system will have a final speed \(\mathrm{u} / 3\) (d) The centre of mass of the system will have a final speed \(u\)

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