A softball player determines her pitching speed by throwing a ball horizontally from an elevation of 20 m above the ground.The ball lands 50 m downrange.What is her pitching speed?
A)5 m/s
B)10 m/s
C)20 m/s
D)25 m/s
E)none of the above

Question

Quizplus · Accepted Answer

We can use the kinematic equation:
y = viy*t + 0.5*a*t^2
where y is the vertical displacement (which is -20m since the ball starts 20m above the ground), viy is the initial vertical velocity (which is 0 since the ball is thrown horizontally), a is acceleration due to gravity (-9.8 m/s^2), and t is time.
Solving for t:
-20m = 0*t + 0.5*(-9.8m/s^2)*t^2
t = sqrt(4.08s^2)
t = 2.02s (rounded to 3 significant figures)
Now we can use the equation:
x = vix*t
where x is the horizontal displacement (which is 50m), and vix is the initial horizontal velocity (which is what we want to find).
Solving for vix:
50m = vix*(2.02s)
vix = 24.8 m/s
Therefore, the pitching speed is approximately 25 m/s.

A Softball Player Determines Her Pitching Speed by Throwing a Ball