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A spring cannon can shoot its projectile at a maximun of 30m/s. what is the maximum height that the projectile will reach? How long will it take to rech that height?

Hint: consider the object's velocity at its maximum height

 Aug 22, 2016
 #1
avatar+118625 
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A spring cannon can shoot its projectile at a maximun of 30m/s. what is the maximum height that the projectile will reach? How long will it take to rech that height?

Hint: consider the object's velocity at its maximum height

 

It will go the highest if it is shot straight up.  (you better not be underneath when id comes back down though.)

 

Gavity is downwards acceleration - it is about 9.8m/s^2

 

\(\ddot y=-9.8\\ \dot y =-9.8t+c\\ \mbox{velocity at t=0 is 30 so c=30}\\ \dot y =-9.8t+30\\ y =-\frac{9.8t^2}{2}+30t+k\\ \mbox{Let the initrial displacement be 0 then k=0}\\ y =-\frac{9.8t^2}{2}+30t\\ \)

the height will  be greatest at the turning point which is where velocity =0

 

\(\begin{align*}-9.8t+30&=0\\ 9.8t&=30\\ t&=\frac{30}{9.8}\\ t&=3.0612\;sec \end{align*}\)

 

\(y=-\frac{9.8t^2}{2}+30t\\ y=-4.9t^2+30t\\ y=-4.*3.0612^2+30*3.0612\\\)

-4*3.0612^2+30*3.0612 = 54.35221824

 

Max height approx 54.35 metres

 Aug 22, 2016
 #2
avatar+36923 
0

Agree with Melody EXCEPT there is a small error in her last line calculation:

-4      *3.0612^2+30*3.0612 = 54.35221824     should be

-4.9   *3.0612^2+30*3.0612 = 54.35221824    resulting in max height of 45.92 m

 Aug 22, 2016

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