Chapter 3, Problem 15Q

Solution

The point which has the least speed in its path of a projectile.

Solution:

At the highest point in its path of a projectile has the least velocity, because at this point vertical component of velocity becomes zero.

Explanation:

The velocity at any point in projectile can be found by the resultant of horizontal and vertical components at that point:

If initial velocity is u , then horizontal component of velocity is: $u_x=u\cos \theta$

Vertical component of velocity: $u_y=u\sin \theta$

If air resistance is negligible, the horizontal component remains constant as there is no acceleration acting in that direction.

In vertical direction, acceleration due to gravity always acts downwards. At highest point, the vertical component of velocity is zero. Thus, at the highest point in trajectory, the projectile will have the least speed which will be equal to the horizontal component of initial velocity.