Using ode45 and differential equations

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Bob 2016-8-8

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https://ww2.mathworks.cn/matlabcentral/answers/298909-using-ode45-and-differential-equations

评论： James Tursa 2016-8-8

A paratrooper steps out of an airplane at a height of 1000 feet and, after five seconds, opens her parachute. Her weight, including her equipment, is 195 pounds. Let y (t) denote her height above the ground after t seconds. Assume that the force due to air resistance is 0.005(y’)^2 pounds while she's in free fall and 0.6(y’)^2 pounds after she opens the chute.

A) At what height does the chute open? B) How long does it take her to reach the ground? C)What is her velocity when she hits the ground? (It's okay if you only know this value within a small range say + or - 0.5 seconds.)

Hint: (a) come up with an appropriate differential equation for before the chute opens, (b) useode45to get an estimate of y(5) and y'(5), (c) come up with an appropriate differential equation for after the chute opens, (d) use the estimate from part (b) as initial conditions for your new differential equation, (e) vary the final time and possibly graph the result until you come up with a reasonable estimate for when she reaches the ground.] I am still very confused on how to get matlab to do this.