Purchase Solution

Velocity of a falling rain drop and air resistance

Not what you're looking for?

Ask Custom Question

Please see the attached file for full problem description. Provide solution for Q7 only.

Q7.

A raindrop is observed at time t=0 when it has mass m and downward velocity u. As it falls under gravity its mass increases by condensation at a constant rate and a resisting force acts on it, proportional to is speed and equal to v when the speed is v.
a) Show that d/dt((M^2)v) = (M^2)g where M = m+ t.
b) Show that the speed of the raindrop at time t is (g/3 )[m+ t-((m^3)/(m+ t)^2)] + ((m^2)u)/(m+ t)^2

Attachments
Purchase this Solution

Solution Summary

This problem is about a falling rain drop, mass of which keeps increasing at a constant rate as it falls against air resistance. I have provided a 4-page solution to the given problem. In order to derive the first relation ship (part a) and to find the time dependence of the rain drop's velocity (part b), it requires a lot of mathematics. I have provided clear and complete solution along with a diagram to this challenging question.

Solution Preview

Following is the text part of the solution. Please see the attached file for complete solution. Equations, diagrams, graphs and special characters will not appear correctly here. Thank you for using Brainmass.
===============================================================================

Consider the situation between the times t and t + dt.

Change in linear momentum dp = (M+ dM)(v + dv) - Mv

dp = M dv + v dM

(Note that dM dv term is ignored since it is very small)

Force = dp/dt = M dv/dt + v dM/dt

But downward force = Mg - λv

Hence,

M dv/dt + v dM/dt = Mg - λv ----------- (1)

But, rate of increase of mass is ...

Purchase this Solution


Free BrainMass Quizzes
Introduction to Nanotechnology/Nanomaterials

This quiz is for any area of science. Test yourself to see what knowledge of nanotechnology you have. This content will also make you familiar with basic concepts of nanotechnology.

Basic Physics

This quiz will test your knowledge about basic Physics.

Variables in Science Experiments

How well do you understand variables? Test your knowledge of independent (manipulated), dependent (responding), and controlled variables with this 10 question quiz.

Classical Mechanics

This quiz is designed to test and improve your knowledge on Classical Mechanics.

The Moon

Test your knowledge of moon phases and movement.