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# Answer: Unless otherwise stated, in the following problems ISBN: 9780321747730 43

## Solution for problem 3E Chapter 3.4

Fundamentals of Differential Equations | 8th Edition

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Problem 3E

Problem

Unless otherwise stated, in the following problems we assume that the gravitational force is constant with g = 9.81 m/sec2 in the MKS system and g = 32 ft/sec2 in the U.S. Customary System.

If the object in Problem 1 has a mass of 500 kg instead of 5 kg, when will it strike the ground? [Hint: Here the exponential term is too large to ignore. Use Newton’s method to approximate the time t when the object strikes the ground (see Appendix B).] Step-by-Step Solution:

Step 1:

In this problem, we have to find the time of the object to hit the ground.

Step 2:

The given values are

Mass : m= 500 kg

Gravitational force :g=9.81 m/s2

Proportionality constant b=50 Ns/m

The buoyancy force (while falling downwards) acts downwards the drags force upwards

Therefore        m =mg-bv ……………..(1)

Step 3:

The general equation for the force Force= mass x acceleration

Where the acceleration is derivative of the velocity i.e a= Therefore

mg-bv=m dt= Therefore we will find the time t by integrating the above equation dt=m  Now we get

t= [ln(mg-bv)-ln(mg)]  ln Taking exponential on both sides of the above equation we get

mg e =mg-bv………..(2)

Step 4 of 5

Step 5 of 5

##### ISBN: 9780321747730

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