The knob of a door always has a larger radius than the shaft so that the distance over which the force is applied in order to the effort force needed to open the door.

The knob of a door always has a larger radius than the shaft so that the distance over which the force is applied is greater in order to reduce the effort force needed to open the door.

Explanation:

A machine makes our work easier by reducing our effort. A door knob is designed in such a way that it reduces the effort force to open the door. A door knob is a simple machine with two parts similar to wheel and axle. The force required to turn the shaft would be greater as compared to turn the knob. The distance over which the force applied increases which reduces the required effort force.

see earlier

the chart show the masses and velocities of two colliding objects that stick together after a collision.

according to the law of conservation of momentum, the momentum of the object after the collision is  

answer

1,500

kg • m/s.