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 General Physics General Physics Help Forum Sep 27th 2018, 10:18 PM #1 Junior Member   Join Date: Sep 2018 Posts: 1 Homework Question Just needed help on this, if anyone could get me the answer on it that would be awesome. Pretend you are standing on top of a tall building and you decide to throw a water balloon down to the sidewalk. If you throw the water balloon with an initial velocity of 12 m/s and the building is 20 m high how long will it take to hit the ground? Assume there is no air resistance. Thanks!   Sep 28th 2018, 01:56 PM #2 Physics Team   Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,347 You should memorize and use the basic equation of linear motion for bodies under constant acceleration: y(t) = y_0 + v_0 t + (1/2)at^2 You may see this equation with different terms, such as using 'x' or 'd' for displacement, or v_i for initial velocity; whatever symbols you're used to you should use; it really doesn't matter which version you use as long as you are consistent. Here you want to solve for time 't' given the initial displacement y_0 = 20m, the final displacement y=0, the initial velocity v_0 = -12 m/s, and acceleration a = g = -9.8m/s^2. By the way, you don't say what the direction is for he initial toss of the water balloon - it makes a big difference! If upward then v_0 = +12 m/s; if downward then v_0 = -12 m/s; if horizontal then v_0 = 0. You can solve for 't' using the quadratic equation. Note that this will give you two answers - one with a positive value for 't' and one with a negative value. The positive value is the correct answer for this problem, but what do you think the negative value of 't' denotes? Post back with your solution and we'll check it for you. Last edited by ChipB; Sep 28th 2018 at 02:04 PM.  Tags acceleration, falling, homework, question 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 fares General Physics 2 Jul 16th 2018 04:58 AM fares General Physics 2 Jul 15th 2018 10:41 AM Edemardil General Physics 2 Jul 12th 2018 03:20 PM marklee Energy and Work 0 Jan 19th 2010 01:23 AM KaylaN Kinematics and Dynamics 1 Sep 2nd 2009 11:43 PM 