Hitting A Target

Classical Mechanics Level pending

The velocity of an arrow shot from a bow is 120 m s \displaystyle 120 \frac{m}{s} at an angle of π 6 \displaystyle \frac{\pi}{6} radians from the horizontal. A target is placed some distance from where the arrow is fired. Assuming the marksman never misses a target, how far is the target from the point where the arrow was fired? Round your answer to the nearest meter.

Assumptions: There is no wind resistance, the terrain is flat and the acceleration due to gravity is 10 m s 2 \displaystyle 10\frac{m}{s^{2}}

2016 873 1026 1247

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1 solution

Brody Acquilano
Jan 14, 2016

Given that the arrow is shot at an angle, we have to break its displacement down into its x and y components using parametric equations.

x = c o s π 6 120 t \displaystyle x=cos\frac{\pi}{6}120t

For y we must also consider the displacement due to gravity.

y = s i n π 6 120 t 1 2 10 t 2 \displaystyle y=sin\frac{\pi}{6}120t-\frac{1}{2}10t^{2}

y = 60 t 5 t 2 \displaystyle y=60t-5t^{2}

y = 5 t ( t 12 ) \displaystyle y=-5t(t-12)

From the factored equation we know that y = 0 y=0 when t = 0 t=0 or t = 12 t=12 . Substitute t = 12 t=12 into the equation for x.

x = c o s π 6 120 ( 12 ) \displaystyle x=cos\frac{\pi}{6}120(12)

x = 1247 \displaystyle x=1247

its helpful thanks and make it more clear

Rafeequa fathima - 2 years, 11 months ago

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