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A projectile is launched with a velocity of $30 \, m/s$ at $40^\circ$ to the ground. To two decimal places, what is its horizontal velocity in $m/s$?

A ball is thrown downward from the top of a $20\, m$ tall building with an initial velocity of $15 \,m/s$. What equation could be used to model its height, $h(t)$?

What is the solution for theses two questions? What steps do you use to solve them? Help is greatly appreciated.

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    $\begingroup$ 4 upvotes? Why? $\endgroup$
    – N.S.JOHN
    May 20, 2016 at 3:05

1 Answer 1

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  1. Typically with physics questions with projectiles the angle is given with respect to the horizontal, so you have $$ v_x = v \cos(\theta) $$ $$ v_y = v \sin(\theta) $$ In this case, you have $$ v_x = 30 \cos(40^\circ) $$

  2. With constant acceleration and an initial velocity, $$ \Delta y = v_i t + \frac{1}{2}g t ^2 $$

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  • $\begingroup$ how did you get that solution for 2? $\endgroup$
    – Sally
    May 19, 2016 at 21:24
  • $\begingroup$ Well, usually it is simply an equation you are given in physics classes. It is possible to derive it using calculus, by taking the double integral of a constant acceleration. $\endgroup$
    – Carser
    May 19, 2016 at 21:32

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