Question

At the topmost point of a trajectory, its velocity and acceleration are at an angle of

Answer 1

At the top most point,

- only x-component of the velocity exists. So velocity is horizontal.

- acceleration is g which acts vertically downward.

Thus, angle between them is 90 degrees.

Answer 2

Solution,

From the attached figure, it is clear that the velocity of projection is $v_o$. If we resolve then in x and y components we get :

$v_x=v_o\cos\theta\\\\v_u=v_o\sin\theta$

P is the topmost point of a trajectory. At P,

$v_y=0$ (At maximum height velocity is 0)

And horizontal velocity will remain the same.

At every point, the acceleration is equal to g and it acts in a downward direction. So, the velocity and acceleration make an angle of 90 degrees. Hence,  at the topmost point of a trajectory, its velocity and acceleration are at an angle of  90 degrees.