An object of mass 2.00 kg is held at a position A, a vertical height of 20.0 m a

Question

An object of mass 2.00 kg is held at a position A, a vertical height of 20.0 m above the ground. Point B is 8.00 m directly below A. Neglect air resistance and use g = 10.0 m/s2. 14) What is the speed of the object at position B when it falls from position A? (A) 10.2 m/s (B) 11.1 m/s (C) 11.9 m/s (D) 12.6 m/s 15) What is the speed of the object just before it touches the ground? (A) 10.0 m/s (B) 12.0 m/s (C) 20.0 m/s (D) There is not enough information to answer this question. 16) What is the ratio of the total energy of the object at position A to position B? (A) 1:1 (B) 2:1 (C) 1:2 (D) 1:6

Explanation / Answer

14) Answer D is correct vf*2 - vo*2 = 2ad vf*2 - 0 = 2(10)(8) vf = 12.6 m/s 15) What is the speed of the object just before it touches the ground? Answer C is correct! Given: d = 20 Infer: a = g = 10 vi = 0 What are you solving for? vf = ? Now that you have four variables, you can solve. Side note: The mass is irrelevant because neglecting air resistance, all objects fall at the same rate. Point B is irrelevant because the object is falling from A to the ground. Also note that we have enough info to solve, so the answer is not D. Anyway, now decide which equation to use: d = vi * t + 1/2 * a * t^2 (no vf) vf = vi + a * t (no d) d = (vi + vf) / 2 * t (no a) vf^2 = vi^2 + 2 * a * d (no t) Use the last one because you do not have the time. vf^2 = vi^2 + 2 * a * d Plug in the variables: vf^2 = 0^2 + 2 * 10 * 20 vf^2 = 400 vf = 20 m/s 16) Answer C is correct

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