Application of First-Order Differential Equations 1. A body falls from

percibaa8

percibaa8

Answered question

2021-12-29

Application of First-Order Differential Equations 1. Any time a body leaves its resting position, it encounters resistance proportional to the cube of the speed. Find the time needed to reach a speed of 2 m/s if the limiting speed is 3 m/s.

Answer & Explanation

usumbiix

usumbiix

Beginner2021-12-30Added 33 answers

Step 1 
It is assumed that resistance is proportional to the speed's cube at all times.
F=Cv3 
At the limiting speed v03 is 3m/s, the force F balances the weight of the body. 
Cv03=mg 
C=mgv03 
The forces in equilibrium is, 
mgF=ma 
mgCv3=mdv dt  
mgmgv03v03=mdv dt  
Step 2 
Reduce the complexity of the equation to determine the time needed to reach a 2 m/s speed.
ggv03=dv dt  
g dt v03=dv(v03v3) 
04g dt 33=02dv(33v3) 
9.8127t=0.0807 
t=0.0807×279.81 
=0.22sec 

trisanualb6

trisanualb6

Beginner2021-12-31Added 32 answers

Step 1
(Note: We are entitled to solve only one question at a time.)
Given:
A body falls from the rest against a resistance propotional to the cube of the speed at any instant.
To Find:
If the limiting speed is 3m/s, find the time required to attain a speed of 2m/s.
Step 2
Explanation:
Let F be the resistance force acting on the body and v be the speed of the body and resistance acting on the body is proportional to cube of speed.
F=Cv3 (i)
where C is proporanaility constant direction of force is upward and v0=3ms is the limiting speed at the limiting speed the force F, balances the weight of the body
Cv03=mg
C=mgv03 (ii)
Now, at any instant of time t, the speed is v mgF=ma, where a : acceleration
mgCv3=mdvdt
g(v03v3v03)=dvdt
9.8v03dt=dvv03v3
put v0}=3 in above, we get
9.827dt=dvv03v3
integrating both side we get
0t9.827dt=02dv(3)3v3
0.363t=0.0807
t=0.22sec
Step 3
Answer:
The time required to attain the speed of 2m/s is 0.22 sec.
karton

karton

Expert2022-01-09Added 613 answers

F=Cv3Cv03=mgC=mgv03mgF=mamgCv3=mdvdtmgmgv03v03=mdvdtggv03=dvdtgdtv03=dv(v03v3)04gdt33=02dv(33v3)9.8127t=0.0807t=0.0807×279.81=0.22sec

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