Question

A football is kicked with a speed of 22 m/s at an angle of ${60}^o$ , with the positive x direction taken along horizontal. At that instant, an observer moves past the football in a car that moves with a constant speed of 11 m/s in the positive x direction. Take +ve y direction vertically upwards.$(g=10m/s^2)$

• A. The initial velocity of the ball relative to the observer in the car is $11\sqrt{3}$ m/s in the +y direction
• B. The initial velocity of the ball relative to the observer in the car is 17 m/s at 60 to the +x direction.
• C. According to the observer in the car, the ball will follow a path that is straight up and down in the y direction.
• D. According to the observer in the car, the ball will follow a straight line that is angled (less than 90) with respect to the observer.

Answer 1

Answer: (A), (C)

The correct options are
A The initial velocity of the ball relative to the observer in the car is $11\sqrt{3}$ m/s in the +y direction
C According to the observer in the car, the ball will follow a path that is straight up and down in the y direction.

Break the velocity into its components along x-axis and y-axis
w.r.t. to observer velocity of football along x direction (Vx) $=0$,
So Motion of the ball as seen from observer will be purely vertical with initial velocity $11\sqrt{3}$upwards.