A projectile is fired with a speed u at an angle thetaθ with the horizontal. Its speed when its direction of motion makes an angle alphaα with the horizontal is?

A: usecthetasecalphausecθsecα
B: usecthetasinalphausecθsinα
C: ucosthetasecalphaucosθsecα
D: usinthetasecalphausinθsecα
PLEASE EXPLAIN EACH AND EVERY STEP

1 Answer
Aug 7, 2017

Let the velocity of projection of the object be u with angle of projection thetaθ with the horizontal direction.
The vertical component of the velocity of projection is usinthetausinθ and the horizontal component is ucosthetaucosθ

Now if t be the time after the projection of the projectile, its direction of velocity makes angle alphaα with the horizontal.Let the velocity of the projectile after t sec be vv

The vertical component of the velocity after time tt will be vsinalphavsinα

But the horizontal component remains unaltered as ucosthetaucosθ

So vcosalpha=ucosthetavcosα=ucosθ

=>v=1/cosalphaxxucostheta=ucosthetasecalphav=1cosα×ucosθ=ucosθsecα

So option C is accepted