- #1
Tchao
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Homework Statement
a. If a ball is launched straight upwards from the ground with an initial velocity of 20.0 m/s, how long does the ball take to reach a height of 15.0 m on the way up?
b. For the same situation, at what time does the ball reach 15.0 m on the way back down?
c. If a ball is dropped from a height of 100.0 m, what is it's height above the ground (in meters) after 3.0 s?
d. If a ball is dropped from a height of 100.0 m, what is it's velocity (in m/s) after 3.00 s? You may treat downward velocity as positive.
Homework Equations
Vx = V0x + axt
x= x0 +v0xt + 1/2axt^2
The Attempt at a Solution
a. 15 = 20t - 4.9t^2
I took the derivative of my equation.
15 = 20 - 9.8t
t = 0.510 s
b. 0 = 20t - 4.9t^2
I assume the height from problem a cancels out with problem b giving 0 and I also took the derivative of equation.
0 = 20 - 9.8t
t= 2.04 s
c. x = 100 - 4.9t^2
Plug in 3.0 s for t.
x = 55.9 m
d. Vx = 9.8 x 3.0 = 29.4 m/s