Question

An arrow is shot straight up in the air at an initial speed of 15.0 m/s. After how much time is the arrow moving downward at a speed of 8.00 m/s?

Answer 1

t = 2.34 s

Step-by-step explanation:

As we know that

initial velocity is 15 m/s upwards

final velocity is 8 m/s downwards

acceleration is due to gravity which is given as g = 9.8 m/s/s in downwards direction

now we can find the time to change the velocity using equation of kinematics

`v_f - v_i = at`

here we need to plug in all data

`(-8) - 15 = (-9.81) t`

`t = (-23)/(-9.81)`

`t = 2.34 s`

so it will take t = 2.34 s

Answer 2

Let us first calculate the speed of the arrow going upwards.
Initial velocity = 15 m/s
Final velocity = 0 m/s
Let us assume the time taken = t
Then
0 = 15 - 9.8t
9.8t = 15
t = 15/9.8
= 1.53 second
Now
Let us calculate the speed of the arrow going downwards
Initial speed = 0 m/s
Final speed = 8 m/s
Then
8 = 9.8t
t = 8/9.8
= 0.816 second
Then
Total time = 1.53 + 0.816
= 2.346 second
I hope the answer helps you.