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 Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum Sep 18th 2008, 08:46 PM #1 Junior Member   Join Date: Sep 2008 Posts: 11 Free Falling Object I have been trying to do this problem but I cant seem to get the answer. An object is thrown upwards with a speed of 16 m/s. how long does it take it reach a height of 7.0m on the way up? The answer is .52 sec but I am not getting that answer Last edited by tweedydaf; Sep 18th 2008 at 11:31 PM.   Sep 18th 2008, 09:22 PM #2 Junior Member   Join Date: Apr 2008 Posts: 21 Well, first, you need to document what you know: $\displaystyle v_{y0} = 16 \frac{m}{s}$ $\displaystyle v_{yf} = ?$ $\displaystyle y_0 = 0 m$ $\displaystyle y_f = 7 m$ $\displaystyle t = ?$ $\displaystyle a = -9.8 \frac{m}{s^2}$ Now, you have everything you need to solve for t: The easiest way to do this would be to find the final velocity at 7 m and then solve for time, the first equation we need is a basic kinematic equation: $\displaystyle v_{yf}^2 = v_{y0}^2 + 2(a)(y_f)$ Plug in what we know: $\displaystyle v_{yf}^2 = 16^2 + 2(-9.8)(7)$ $\displaystyle = 256 - 137.2$ $\displaystyle = 119$ $\displaystyle v_{yf} = 10.9 \frac{m}{s}$ Now, we take another equation: $\displaystyle v_{yf} = v_{y0} + at$ Plug what we know: $\displaystyle 10.9 = 16 - 9.8t$ $\displaystyle -5.1 = -9.8t$ $\displaystyle 0.52 s = t$ And there you go.   Sep 18th 2008, 10:33 PM #3 Junior Member   Join Date: Sep 2008 Posts: 11 Thank you so much for the help  Tags falling, free, object Thread Tools Show Printable Version Email this Page Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Similar Physics Forum Discussions Thread Thread Starter Forum Replies Last Post mryeh Electricity and Magnetism 5 Apr 4th 2014 05:54 AM RPSGCC733 Kinematics and Dynamics 2 Aug 22nd 2012 09:18 PM Deadstar Kinematics and Dynamics 2 Apr 5th 2010 12:44 PM Eva Kinematics and Dynamics 25 Oct 12th 2009 12:09 PM colombo Kinematics and Dynamics 1 Sep 6th 2008 09:41 PM