Question

A rod of mass M = 4 kg, length L = 1.8 meters, and moment of inertia ML2/12 is free to move on a frictionless surface. The rod is at rest when a puck of mass m = 0.4 kg approaches with a speed vi = 20 m/s perpendicular to the rod's length and strikes the rod at a point d = 0.3 meters from its lower end. After the collision, the puck moves backward with a speed vf = 10 m/s. The rod's center of mass moves forward with speed v and rotates with angular speed ω. (a) What is the speed v of the rod's center of mass after the collision?

Answer 1

The speed of the rod's center of mass after the collision is 6 m/s.

Step-by-step explanation:

Given that,

Mass of rod = 4 kg

Length l = 1.8 m

Moment of inertia
`I=(ML^2)/(12)`

Mass of puck = 0.4 kg

Initial speed= 20 m/s

Distance = 0.3 m

Final speed = 10 m/s

(a). We need to calculate the speed v of the rod's center of mass after the collision

As there is no external force acting on the system so, linear and angular momentum of the system will be conserved.

Using conservation of momentum

`m_(i)v_(i)=m_(f)v_(f)+Mv`

Put the value into the formula

`0.4*20=-0.4*10+2v`

`v=(8+4)/(2)`

`v=6\ m/s`

Hence, The speed of the rod's center of mass after the collision is 6 m/s.