theorangedog.net

Welcome Back To Calculus

by theorangedog on Jan.02, 2008, under Skills

Problem:
A rock thrown upward with velocity 16 ft/sec reaches height small f = 16t - 16t^2 at time t.
(a) Find its average speed smallDelta f/Delta t from small t = 0 to small t = frac{1}{2}.
(b) Find its average speed smallDelta f/Delta t from small t = frac{1}{2} to small t = 1.
(c) What is small df/dt at small t = frac{1}{2}?

Solution:
To find speed given distance, we need to take the first derivative. Derivatives of polynomials are one of the few things I remember, even though this is covered in the material I’m reading. That equation is: small f^prime (t) = 16 - 32t. However, the question isn’t asking for a limit, so the full equation of smallfrac{Delta f}{Delta t} = frac{f(t+Delta t) - f(t)}{Delta t} should be used. Essentially, it is the average of the first derivative at two given points.
This results in:
(a) 8 ft/sec
(b) -8 ft/sec
(c) 0, as it is the instantaneous point of reversal (this one assumes a limit, as t approaches smallfrac{1}{2})

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