Question

A projectile launched at an angle of ${45}^o$ to the horizontal. Which one of the following statements is true about motion of projectile ? Assume air resistance is negligible.

• A. The acceleration vector points opposite to the velocity vector on the way up and in the same direction as the velocity vector on the way down.
• B. The speed at the top of the trajectory is zero.
• C. The objects total speed remains constant during the entire flight.
• D. The horizontal speed decreases on the way up and increases on the way down
• E. The vertical speed decreases on the way up speed changes. D is false because the horizontal component is constant throughout the motion.

Answer 1

The correct option is E The vertical speed decreases on the way up speed changes. D is false because the horizontal component is constant throughout the motion.

The only external force acting on the object is the gravitational force vertically downwards. Thus the acceleration of the projectile is $g$ downwards always. Thus there is no change in speed of the object in horizontal direction.

The speed of object in vertical direction at the top of the trajectory is zero. However the net speed at the point is equal to the constant horizontal component.

Due to downward constant acceleration, the vertical speed decreases way up, becomes zero and then increases way down. Thus option E is correct.