Fighters, Rockets and Deaf Hunters
Here is some more practice for you in using the equations of motion.
Remember to follow these steps:
1. Draw a sketch: Show the object of interest at the beginning and end of the interval. Assign a
positive direction with a black + arrow. Attach and label all the relevant parameters (color code
‘em!): Δx, vo, vf, a and Δt.
2. If the acceleration is constant, identify the missing variable and select the equation of motion that
goes with it. (If the acceleration not constant, abort the mission!)
3. Solve the equation algebraically first.
4. Finally, plug in the numbers, round to the correct number of sig figs, and check the units.
1. An F-16 fighter is flying forward with a velocity of 300.0 m/s when it fires a
missile straight ahead. The missile immediately accelerates forward with a
constant acceleration of 100.0 m/s2. How far does the missile travel in the
first 5.00 s after being fired? (Complete the side view sketch. Note, vo for the
missile is the same as the velocity of the plane.)
Courtesy: Andrews Air
Force Base
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2. A rocket accelerates uniformly forward from a velocity of 5.0 x 104m/s to a velocity of 2.00 x 105m/s
over a displacement of 1.00 x 109 m. Don’t forget to sketch the rocket in its final position!
a) What is the acceleration of the rocket?
b) How long does it take the rocket to cover this distance? (Which variable should you solve for?)
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3. You are being chased through the forest by a deaf hunter named Elmer who is
convinced that you are the prize-winning buck he has been looking for. He has you
pinned down behind a log 2.00 x 102 m away but Elmer only has one bullet left in his
30-06* rifle. You are wondering if you can stick your face up over the log to draw
his fire and still have time to duck when you see the flash of his gun. Elmer’s gun
shoots bullets with an air speed of 1.00 x 103 m/s (ignore the effects of air resistance
and gravity.) You figure it will take you 0.18 s to duck after you see the flash. Can
you risk sticking your head up? There are multiple ways to solve this problem, choose one!
PS: Do you need to worry about how long it takes light to cover the distance between Elmer’s gun and you?
Why not?
* “30-06” pronounced “thirty-aught-six” is a shorthand reference to the caliber, or diameter of the bullet, in
inches: 0.30”, and the year it was introduced, 1906.
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