Answer:
part (a) v = 1.7 m/s towards right direction
part (b) Not an elastic collision
part (c) F = -228.6 N towards left.
Explanation:
Given,
- Mass of the first puck =
![m_1\ =\ 5\ kg](https://tex.z-dn.net/?f=m_1%5C%20%3D%5C%205%5C%20kg)
- Mass of the second puck =
![m_2\ =\ 3\ kg](https://tex.z-dn.net/?f=m_2%5C%20%3D%5C%203%5C%20kg)
- initial velocity of the first puck =
![u_1\ =\ 3\ m/s.](https://tex.z-dn.net/?f=u_1%5C%20%3D%5C%203%5C%20m%2Fs.)
- Initial velocity of the second puck =
![u_2\ =\ -1.5\ m/s.](https://tex.z-dn.net/?f=u_2%5C%20%3D%5C%20-1.5%5C%20m%2Fs.)
Part (a)
Pucks are stick together after the collision, therefore the final velocities of the pucks are same as v.
From the conservation of linear momentum,
![m_1u_1\ +\ m_2u_2\ =\ (m_1\ +\ m_2)v\\\Rightarrow v\ =\ \dfrac{m_1u_1\ +\ m_2u_2}{m_1\ +\ m_2}\\\Rightarrow v\ =\ \dfrac{5\times 3\ -\ 1.5\times 1.5}{5\ +\ 1.5}\\\Rightarrow v\ =\ 1.7\ m/s.](https://tex.z-dn.net/?f=m_1u_1%5C%20%2B%5C%20m_2u_2%5C%20%3D%5C%20%28m_1%5C%20%2B%5C%20m_2%29v%5C%5C%5CRightarrow%20v%5C%20%3D%5C%20%5Cdfrac%7Bm_1u_1%5C%20%2B%5C%20m_2u_2%7D%7Bm_1%5C%20%2B%5C%20m_2%7D%5C%5C%5CRightarrow%20v%5C%20%3D%5C%20%5Cdfrac%7B5%5Ctimes%203%5C%20-%5C%201.5%5Ctimes%201.5%7D%7B5%5C%20%2B%5C%201.5%7D%5C%5C%5CRightarrow%20v%5C%20%3D%5C%201.7%5C%20m%2Fs.)
Direction of the velocity is towards right due to positive velocity.
part (b)
Given,
Final velocity of the second puck = ![v_2\ =\ 2.31\ m/s.](https://tex.z-dn.net/?f=v_2%5C%20%3D%5C%202.31%5C%20m%2Fs.)
Let
be the final velocity of first puck after the collision.
From the conservation of linear momentum,
![m_1u_1\ +\ m_2u_2\ +\ m_1v_1\ +\ m_2v_2\\\Rightarrow v_1\ =\ \dfrac{m_1u_1\ +\ m_2u_2\ -\ m_2v_2}{m_1}\\\Rightarrow v_1\ =\ \dfrac{5\times 3\ -\ 1.5\times 1.5\ -\ 1.5\times 2.31}{5}\\\Rightarrow v_1\ =\ 1.857\ m/s.](https://tex.z-dn.net/?f=m_1u_1%5C%20%2B%5C%20m_2u_2%5C%20%2B%5C%20m_1v_1%5C%20%2B%5C%20m_2v_2%5C%5C%5CRightarrow%20v_1%5C%20%3D%5C%20%5Cdfrac%7Bm_1u_1%5C%20%2B%5C%20m_2u_2%5C%20-%5C%20m_2v_2%7D%7Bm_1%7D%5C%5C%5CRightarrow%20v_1%5C%20%3D%5C%20%5Cdfrac%7B5%5Ctimes%203%5C%20-%5C%201.5%5Ctimes%201.5%5C%20-%5C%201.5%5Ctimes%202.31%7D%7B5%7D%5C%5C%5CRightarrow%20v_1%5C%20%3D%5C%201.857%5C%20m%2Fs.)
For elastic collision, the coefficient of restitution should be 1.
From the equation of the restitution,
![v_1\ -\ v_2\ =\ e(u_2\ -\ u_1)\\\Rightarrow e\ =\ \dfrac{v_1\ -\ v_2}{u_2\ -\ u_1}\\\Rightarrow e\ =\ \dfrac{1.857\ -\ 2.31}{-1.5\ -\ 3}\\\Rightarrow e\ =\ 0.1\\](https://tex.z-dn.net/?f=v_1%5C%20-%5C%20v_2%5C%20%3D%5C%20e%28u_2%5C%20-%5C%20u_1%29%5C%5C%5CRightarrow%20e%5C%20%3D%5C%20%5Cdfrac%7Bv_1%5C%20-%5C%20v_2%7D%7Bu_2%5C%20-%5C%20u_1%7D%5C%5C%5CRightarrow%20e%5C%20%3D%5C%20%5Cdfrac%7B1.857%5C%20-%5C%202.31%7D%7B-1.5%5C%20-%5C%203%7D%5C%5C%5CRightarrow%20e%5C%20%3D%5C%200.1%5C%5C)
Therefore the collision is not elastic collision.
part (c)
Given,
Time of impact = t = ![25\times 10^{-3}\ sec](https://tex.z-dn.net/?f=25%5Ctimes%2010%5E%7B-3%7D%5C%20sec)
we know that the impulse on an object due to a force is equal to the change in momentum of the object due to the collision,
![\therefore I\ =\ \ m_1v_1\ -\ m_1u_1\\\Rightarrow F\times t\ =\ m_1(v_1\ -\ u_1)\\\Rightarrow F\ =\ \dfrac{m_1(v_1\ -\ u_1)}{t}\\\Rightarrow F\ =\ \dfrac{5\times (1.857\ -\ 3)}{25\times 10^{-3}}\\\Rightarrow F\ =\ -228.6\ N](https://tex.z-dn.net/?f=%5Ctherefore%20I%5C%20%3D%5C%20%5C%20m_1v_1%5C%20-%5C%20m_1u_1%5C%5C%5CRightarrow%20F%5Ctimes%20t%5C%20%3D%5C%20m_1%28v_1%5C%20-%5C%20u_1%29%5C%5C%5CRightarrow%20F%5C%20%3D%5C%20%5Cdfrac%7Bm_1%28v_1%5C%20-%5C%20u_1%29%7D%7Bt%7D%5C%5C%5CRightarrow%20F%5C%20%3D%5C%20%5Cdfrac%7B5%5Ctimes%20%281.857%5C%20-%5C%203%29%7D%7B25%5Ctimes%2010%5E%7B-3%7D%7D%5C%5C%5CRightarrow%20F%5C%20%3D%5C%20-228.6%5C%20N)
Negative sign indicates that the force is towards in the left side of the movement of the first puck.