Question

Particle is thrown with speed 'u' making an angle 'alpha' horizontal from the ground . After how much time velocityof particle make angle with theta with horizontal.

Answer 1

Let the horizontal component of both the velocities at point making an angle a (velocity u) and at point making an angle b (say velocity v) is given as,

ux=ucosavx=vcosb
In a projectile motion, the horizontal component is always same at every point. Thus we get,
ucosa=vcosbv=ucosacosb