Answer:
Start of the motion: 2 seconds
End on the motion: 1 second
Explanation:
The force acting on a body in free fall is the gravitational force
The approximate time at which the upward speed of the ball will be 20 m/s is 1.942 second
The approximate time at which the upward speed of the ball will be 30 m/s is 0.923 second
Question: Please find attached the required speedometer readings that can be used to complete the question
Reasons:
Known parameter;
The direction in which the ball is launched = Straight upward
The speedometer reading after 5 seconds = 10 m/s moving downward
Required:
The time at which the ball will be moving upwards with a velocity of 20 m/s, and 30 m/s
Solution:
Taking upwards as positive, the formula for velocity is given as follows;
v = u - g·t
Where;
v = The speed of the ball = -10 m/s (downward is negative)
g = Acceleration due to gravity ≈ 9.81 m/s²
u = The initial speed of the ball
-10 = u - 9.81 × 5
∴ u = -10 + 9.81 × 5 = 39.05
The initial upward speed of the ball at the time of launch, u = 39.05 m/s
The time at which the upward speed of the ball will be 20 m/s, we have;
v = 20 = u - g·t
∴ 20 = 39.05 - 9.81×t
[tex]t = \dfrac{20 - 39.05}{-9.81} =1\frac{308}{327} \approx 1.942[/tex]
The time at which the ball will be moving upwards at a speed of 20 m/s is t ≈ 1.942 s
Upward speed of 30 m/s
When the ball is moving upwards with a speed of 30 m/s, we have;
30 = 39.05 - 9.81 × t
[tex]t = \dfrac{30 - 39.05}{-9.81} = \dfrac{905}{981} \approx 0.923[/tex]
The time at which the ball will be moving upwards at a speed of 30 m/s is t ≈ 0.923 s
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