The horizontal and vertical components of the initial velocity of a football are 16 m/s and 20 m/s respectively.If there is no air resistance,how long does it take the football to reach the top of its trajectory?
A)1.0 s
B)2.0 s
C)3.0 s
D)4.0 s
E)5.0 s

Question

Quizplus · Accepted Answer

We can use the fact that the time taken for an object to reach the top of its trajectory is half of the total time for the entire trajectory. 
The vertical component of velocity at the top of the trajectory is zero, so we can use the equation v = u + at to find the time taken for the football to reach the top of its trajectory: 
0 = 20 - 9.81t 
t = 2.04 s (rounded to 2 decimal places). 
Therefore, the total time for the trajectory is twice this value: 
total time = 2 x 2.04 s = 4.08 s (rounded to 2 decimal places). 
The closest answer choice is B, which is 2.0 s.

The Horizontal and Vertical Components of the Initial Velocity of a Football