Drexel dragonThe Math ForumDonate to the Math Forum

Ask Dr. Math - Questions and Answers from our Archives
_____________________________________________
Associated Topics || Dr. Math Home || Search Dr. Math
_____________________________________________

How Long Until the Bomb Hits the Ground?


Date: 8/25/96 at 13:42:16
From: Anonymous
Subject: Plane Drops Bomb....

A bomber flying at 32,000 feet over level terrain drops a 500-pound 
bomb.

a. How long will it take the bomb to strike the ground?
Using the position equations s = -16t^2 +vt + s 
I got an answer of 44.721 seconds before impact.

My first question is, how does the weight of the falling object factor 
into the velocity at which it is falling, since it is reasonable to 
assume an object of a heavier mass would fall at faster rate.

b. If the plane is flying at 600 mph how far will the bomb travel 
horizontally during its descent?

This is the part of the problem that is giving the most concern.
If the bomb is being dropped out of the plane, would not the force of 
gravity and the tendency for the bomb to fall be greater than the 
velocity of the plane carrying it, therefore causing it to fall 
straight down? However, it could also be reasoned that if it takes 
44.721 seconds for the bomb to hit the ground then it is falling at 
approximatlely 715.54 ft per second. So during the first second would 
it still be travelling with the velocity of the plane and would have 
travelled 10 miles in the first second [600mph/60sec].


Date: 8/25/96 at 15:25:5
From: Doctor Robert
Subject: Re: Plane Drops Bomb...

In the absence of air resistance (which is only really valid outside 
the atmosphere) all bodies accelerate at the same rate when falling in 
the earth's gravitational field.  The reason for this is that the 
FORCE that the earth exerts on a mass is proportional to that object's 
mass, while the acceleration that the object experiences is inversely 
proportional to its mass, so that the mass of the object cancels out.  
So, in the absence of air resistance, a feather and a ton of bricks 
accelerate at the same rate!

Your value of 44.7 seconds for the time of fall is correct.

When the bomb was dropped from the plane, it (the bomb) was traveling 
at 600 mph.  Again, if we neglect air resistance, we can say that the 
bomb was traveling at 600 miles per HOUR for 44.7 seconds.  How far 
did it travel?

  D = rate times time = 600 miles/hour times 44.7/3600 hours

   which is approximately = to 7.45 miles.

I hope that this helps.

-Doctor Robert,  The Math Forum
 Check out our web site!  http://mathforum.org/dr.math/   
    
Associated Topics:
High School Physics/Chemistry

Search the Dr. Math Library:


Find items containing (put spaces between keywords):
 
Click only once for faster results:

[ Choose "whole words" when searching for a word like age.]

all keywords, in any order at least one, that exact phrase
parts of words whole words

Submit your own question to Dr. Math

[Privacy Policy] [Terms of Use]

_____________________________________
Math Forum Home || Math Library || Quick Reference || Math Forum Search
_____________________________________

Ask Dr. MathTM
© 1994-2013 The Math Forum
http://mathforum.org/dr.math/