A particle is projected from ground with initial velocity u at an angle theta to the horizontal find out velocity of the particle when the direction of the motion is at an angle Alpha to the horizontal

When the ball is projected wth velocity u it has 2 components of velocity,one along horizontal ie.u cos theta and the second component along vertical direction u sin theta. Also tge velocity at the point where the angle is alpha will have two components v cos alpha and v sin alpha. Now you nay know that the horizontal component of velocity remains constant the projectile,a nd hence we can say that- u cos theta = v cos alpha