Answer:
The time the ball it takes to have the downward speed 4 m/s is 1.22 sec.
Step-by-step explanation:
Lets explain the motion of the ball
The ball is kicked straight upwards with an initial vertical speed of 8.0 m/s
Its velocity decreases util it reaches the maximum height
At the maximum height its velocity is equal to zero
Then it fall down to the ground
We can ignore air resistance
Lets find the time it takes the ball to reach the maximum height
The acceleration of gravity is -9.8 m/s²
The initial velocity is 8 m/s upward
The final velocity is zero
So lets use the rule v = u + gt, where v is the final velocity, u is the initial
velocity, g is the acceleration of gravity and t is the time
u = 8 , v = 0 , g = -9.8
Substitute these value in the equation above
0 = 8 - 9.8 t
Add 9.8 t for both sides
9.8 t = 8
Divide both sides by 9.8
t = 40/49 seconds
The ball falls withe initial velocity zero and increases to reach 4 m/s
The velocity 4 m/s is downward
The acceleration of gravity is 9.8 m/s²
By using the same rule
u = 0 , v = 4 , g = 9.8
4 = 0 + 9.8 t
4 = 9.8 t
Divide both sides by 9.8
t = 20/49
The time the ball it takes to have the downward speed 4 m/s is the sum
of the two times above
The time the ball it takes =
seconds
The time the ball it takes to have the downward speed 4 m/s is 1.22 sec.