If an object is thrown upward, dropped, or thrown downward and travels in a straight line subject only to gravity, the height \( h \) of the object above the ground (in feet) after \( t \) seconds is given by \( h=-16 t^{2}+v_{0} t+h_{0} \), where \( h_{0} \) is the height of the object when \( t=0 \) and \( v_{0} \) is the velocity of the object at time \( t=0 \). Note that an object that is dropped (rather than thrown downward) has initial velocity \( v_{0}=0 \) You are standing on a cliff that is 200 feet high. How long will it take a rock to reach the ground if (a) you drop it? (b) you throw it downward at an initial velocity of 40 feet per second? (c) How far does the rock fall in 2 seconds if you throw it downward with an initial velocity of 40 feet per second? (a) A rock will take \( \square \) seconds to reach the ground if you drop it from 200 feet. (Type an integer or decimal rounded to two decimal places as needed.) (b) A rock will take \( \square \) seconds to reach the ground if you throw it downward at an initial velocity of 40 feet per second from 200 feet. (Type an integer or decimal rounded to two decimal places as needed.) (c) If you throw the rock downward with an initial velocity of 40 feet per second, then it falls \( \square \) feet in 2 seconds. (ther
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Beyond the Answer
To find the time it takes for the rock to reach the ground when dropped from a height of 200 feet: (a) When dropped, \( v_{0} = 0 \) and \( h_{0} = 200 \). The equation becomes: \[ h = -16t^2 + 200 \] Setting \( h = 0 \) to find when it hits the ground: \[ 0 = -16t^2 + 200 \] This solves to \( t^2 = 12.5 \), so \( t = \sqrt{12.5} \approx 3.54 \) seconds. (b) When thrown downward at 40 feet per second, the initial velocity \( v_{0} = 40 \): \[ h = -16t^2 + 40t + 200 \] Setting \( h = 0 \): \[ 0 = -16t^2 + 40t + 200 \] Using the quadratic formula, we find \( t \approx 5.54 \) seconds. (c) To determine how far the rock falls in 2 seconds with an initial velocity of 40 feet per second: Using \( h(t) = -16(2)^2 + 40(2) + 200 \): \[ h(2) = -64 + 80 + 200 = 216 \] It falls from 200 to 216, meaning it falls \( 216 - 200 = 16 \) feet during those 2 seconds. So, the answers are: (a) A rock will take \( 3.54 \) seconds to reach the ground if you drop it from 200 feet. (b) A rock will take \( 5.54 \) seconds to reach the ground if you throw it downward at an initial velocity of 40 feet per second from 200 feet. (c) If you throw the rock downward with an initial velocity of 40 feet per second, then it falls \( 16 \) feet in 2 seconds.
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