Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

The distance $s$ in feet that a thrown object will fall in $t$ seconds is given by

$$s=16t^2 + vt\;,$$

where $v$ is the initial downward velocity in feet/second. Find the initial velocity of an object that falls $80$ feet in $2$ seconds.

share|cite|improve this question
What have you done? Where are you stuck? – Pragabhava Nov 13 '12 at 1:14

Hint: you have three unknowns in the equation and are provided values for two of them.

share|cite|improve this answer

So you have

  • $s =$ distance
  • $v =$ initial velocity
  • $t =$ time.

You have these related via: $$ s = 16t^2 + tv. $$

Now if the distance $d= 80$ (feet) and the time is $t = 2$ (sec.), you know two of the three variables, so you can solve for the third. I.e., start with $$ 80 = 16(2)^2 + 2v. $$ This is a (linear) equation with just one unknown that you can solve for.

share|cite|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.