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TAKEN-FROM-REAL-LIFE-if-I-try-to-walk-into-a-shop-through-a-super-clean-closed-glass-door-and-get-myself-a-bloody-nose-then-what-s-the-value-of-the-brake-acceleration-when-we-assume-1-my-walking-spee




Question Number 161194 by MJS_new last updated on 14/Dec/21
TAKEN FROM REAL LIFE  if I try to walk into a shop through a super  clean closed glass door and get myself a  bloody nose then what′s the value of the  brake acceleration when we assume  1) my walking speed is 7km/hr  2) the crumple zone of my nose is 1/2′′  3) the brake acceleration is constant
$$\mathbb{TAKEN}\:\mathbb{FROM}\:\mathbb{REAL}\:\mathbb{LIFE} \\ $$$$\mathrm{if}\:\mathrm{I}\:\mathrm{try}\:\mathrm{to}\:\mathrm{walk}\:\mathrm{into}\:\mathrm{a}\:\mathrm{shop}\:\mathrm{through}\:\mathrm{a}\:\mathrm{super} \\ $$$$\mathrm{clean}\:\mathrm{closed}\:\mathrm{glass}\:\mathrm{door}\:\mathrm{and}\:\mathrm{get}\:\mathrm{myself}\:\mathrm{a} \\ $$$$\mathrm{bloody}\:\mathrm{nose}\:\mathrm{then}\:\mathrm{what}'\mathrm{s}\:\mathrm{the}\:\mathrm{value}\:\mathrm{of}\:\mathrm{the} \\ $$$$\mathrm{brake}\:\mathrm{acceleration}\:\mathrm{when}\:\mathrm{we}\:\mathrm{assume} \\ $$$$\left.\mathrm{1}\right)\:\mathrm{my}\:\mathrm{walking}\:\mathrm{speed}\:\mathrm{is}\:\mathrm{7km}/\mathrm{hr} \\ $$$$\left.\mathrm{2}\right)\:\mathrm{the}\:\mathrm{crumple}\:\mathrm{zone}\:\mathrm{of}\:\mathrm{my}\:\mathrm{nose}\:\mathrm{is}\:\mathrm{1}/\mathrm{2}'' \\ $$$$\left.\mathrm{3}\right)\:\mathrm{the}\:\mathrm{brake}\:\mathrm{acceleration}\:\mathrm{is}\:\mathrm{constant} \\ $$
Commented by mr W last updated on 14/Dec/21
a=(v^2 /(2s))  v=7 kmh=(7/(3.6)) m/s  s=1/2′′=((0.054)/2) m  a=70 m/s^2  ≈7 g
$${a}=\frac{{v}^{\mathrm{2}} }{\mathrm{2}{s}} \\ $$$${v}=\mathrm{7}\:{kmh}=\frac{\mathrm{7}}{\mathrm{3}.\mathrm{6}}\:{m}/{s} \\ $$$${s}=\mathrm{1}/\mathrm{2}''=\frac{\mathrm{0}.\mathrm{054}}{\mathrm{2}}\:{m} \\ $$$${a}=\mathrm{70}\:{m}/{s}^{\mathrm{2}} \:\approx\mathrm{7}\:{g} \\ $$

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