word problem

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TinyTim

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A ball is thrown vertically upward from the ground at a velocity of 92 feet per second. Its distance from the ground after t seconds is given by s(t) = -16t^2 + 92t. How fast is the ball moving 3 seconds after being thrown?

a. -4 ft per sec
b. -13 ft per sec
c. 44 ft per sec
d. 132 ft per sec

I dont know where to start.
 
Since this is a Calculus problem, I believe you have to take the derivative. Let t = 3, so we have s(t)= -32 *3 + 92 = -4.
 
TinyTim said:
A ball is thrown vertically upward from the ground at a velocity of 92 feet per second. Its distance from the ground after t seconds is given by s(t) = -16t^2 + 92t. How fast is the ball moving 3 seconds after being thrown?

a. -4 ft per sec
b. -13 ft per sec
c. 44 ft per sec
d. 132 ft per sec

I dont know where to start.
Click to expand...
Velocity is the derivative of displacement, so differentiate s(t). Then substitute the given time to find the ball's velocity at t=3.
 
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