Question

A projectile is fired with velocity V making the angle x with the horizontal. what is the change in velocity when it is at the highest point?

At the highest point the velocity of the object will be u cos(x). And intially the velocity will be u. And u = root (u²sin²x+u²cos²x).

Now required ∆u= u cos x - u

Here we cannot say, because the horizontal component of velocity remains constant And only the vertical component of velocity changes, that u sin x vanishes, so ∆u=u sin x. Because u is not equal to u sin x + u cos x, but is equal to the resultant of u sin x and u cos x. But in the test in the projectile chapter my answer tuemed out to be Wrong. Why?

Answer 1

If you have written delta u = u sin x...
its wrong...this only deals with the vertical part of velocity not the horizontal component.
when we consider about velocity, both component wants to be taken for consideration....
your answer only takes the change in the vertical component only.

si correct is delta u= u.cos x - u....

LIKE IF SATISFIED...