The quantity that has a magnitude of zero when the ball is at the highest point in its trajectory is
the vertical velocity.
In fact, the motion of the ball consists of two separate motions:
- the horizontal motion, on the x-axis, which is a uniform motion with constant velocity

, where

- the vertical motion, on the y-axis, which is a uniformly accelerated motion with constant acceleration

directed downwards, and with initial velocity

. Due to the presence of the acceleration g on the vertical direction (pointing in the opposite direction of the initial vertical velocity), the vertical velocity of the ball decreases as it goes higher, up to a point where it becomes zero and it reverses its direction: when the vertical velocity becomes zero, the ball has reached its maximum height.
Friction is the force that acts on an object and opposes its motion
downward force then reaction if you mean what forces
Answer:
(A) Original speed= 9.22 m/s
(B) Acceleration= -1.0099 m\s^2
Explanation:
A truck covers 40m in 7.10 secs
The truck slows down at a uniform velocity of 2.05 m/s
(A) The original speed can be calculated as follows
Vo= 2(40)/7.10 - 2.05
= 80/7.10 - 2.05
= 11.2676 - 2.05
= 9.22m/s
(B) The acceleration can be calculated as follows
a= Vf-Vo/t
= 2.05-9.22/7.10
= -7.17/7.10
= -1.0099m/s^2