The drawing shows a device that you can make with a piece of cardboard, which ca

Question

The drawing shows a device that you can make with a piece of cardboard, which can be used to measure a person's reaction time. Hold the card at the top and suddenly drop it. Ask a friend to try to catch the card between his or her thumb and index finger. Initially, your friend's fingers must be level with the asterisks at the bottom. By noting where your friend catches the card, you can determine his or her reaction time in milliseconds (ms). Calculate the distances d1 = 60 ms, d2 = 120 ms, and d3 = 180 ms.
d1 = 1 cm _hold here______
d2 = 2 cm d3_____ #####
d3 = 3 cm #####
d2 _____ #####
#####
d1 _____ #####
______

Explanation / Answer

Let: t be the time in seconds from when the card is released, s cm be the distance it has fallen, g be the accleration (981 cm/sec^2) due to gravity. The equation is: s = gt^2 / 2 60 ms = 0.06 sec. 120 ms = 0.12 sec. 180 ms = 0.18 sec. If d1, d2 and d3 are the distances fallen: d1 = 981 * 0.06^2 / 2 = 1.77 cm. d2 = 981 * 0.12^2 / 2 = 7.06 cm. d3 = 981 * 0.18^2 / 2 = 15.9 cm.

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