A 0.5 kg ball moving with a speed of 12 m/s strikes a hard wall at an angle of 30° with the wall. It is reflected with the same speed and at the same angle. If the ball is in contact with the wall for 0.25 s, the average force acting on the wall is
The vector represents the momentum of the object before the collision, and the vector that after the collision. The vector represents the change in momentum of the object .
As the magnitudes of are equal, the components of along the wall are equal and in the same direction, while those perpendicular to the wall are equal and opposite. Thus, the change in momentum is due only to the change in direction of the perpendicular components. Hence,
Its time rate will appear in the form of average force acting on the wall.
A uniform rod of length l and mass m is free to rotate in a vertical plane about A. The rod initially in horizontal position is released. The initial angular acceleration of the rod is: (Moment of inertia of rod about A is )
The moment of inertia of the uniform rod about an axis through the end and perpendicular to length is
where m is mass of rod and l its length. Torque acting on centre of gravity of rod is given by
Two cars moving in opposite directions approach each other with speed of 22 m/s and 16.5 m/s respectively. The driver of the first car blows a horn having a frequency 400 Hz. The frequency heard by the driver of the second car is [velocity of sound 340 m/s]