# SOLUTION: An object is propelled vertically upward with an initial velocity of 20 meters per second. The distance s (in meters) of the object from the ground after t seconds is s = -4.9t^2 +

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 Question 160112: An object is propelled vertically upward with an initial velocity of 20 meters per second. The distance s (in meters) of the object from the ground after t seconds is s = -4.9t^2 + 20t. (a) When will the object be 15 meters above the ground? (b) When will it strike the ground? (c) Will the object reach a height of 100 meters?Answer by stanbon(57323)   (Show Source): You can put this solution on YOUR website!An object is propelled vertically upward with an initial velocity of 20 meters per second. The distance s (in meters) of the object from the ground after t seconds is s(t) = -4.9t^2 + 20t. --------- The equation tells you how far above the ground the object after "t" seconds. I'll just point out the equations you should solve: -------------------- (a) When will the object be 15 meters above the ground? Solve -4.9t^2 + 20t = 15 You should get two solutions: one for the time as it rises and one for the time it is decending.. -------------------------------------- (b) When will it strike the ground? Solve -4.9t^2 + 20t = 0 You should get twon solutions. One of the solutions is t=0. ------------------------------------ (c) Will the object reach a height of 100 meters? Solve -4.9t^2 + 20t = 100 Two solutions. ================= Cheers, Stan H.