Given the following, with the correct answer. What type of formula would be applied to this problem and how so?
An object falls freely in a straight line and experiences air resistance proportional to its speed; this means its acceleration is a(t)=−kv(t), where k is a positive constant and v is the object's velocity. The speed of the object decreases from 1300 ft/s to 1200 ft/s over a distance of 1400 ft. Approximate the time required for this deceleration to occur.
I attempted to use the formula (1300^2 - 1200^2) / 1400^2 as suggested but it does not give the correct answer.
Correct Answer is: 1.1206
The units of your calculation are sec$^{-2}$ so that formula cannot be right. As a simple approximation, the average speed is about $1250$ ft/sec, so the deceleration time is $1400/1250=1.12$ seconds. For more accuracy, you should solve $s=\frac 12at^2+v_0t$ with your data which will lower the average speed slightly and increase the time slightly.