UPSC Exam  >  UPSC Notes  >  Mathematics Optional Notes for UPSC  >  Rectilinear Motion

Rectilinear Motion | Mathematics Optional Notes for UPSC PDF Download

Download, print and study this document offline
Please wait while the PDF view is loading
 Page 1


Edurev123 
Dynamics & Statics 
1. Rectilinear Motion 
1.1 One end of a light elastic string of natural length ?? and modulus of elasticity 
?????? is attached to a fixed point ?? and the other end to a particle of mass ?? . The 
particle initially held at rest at ?? is bit fall. Find the greatest extension of the string 
during motion and show that the particle will reach ?? again after a time. 
(?? +?? -?????? -?? ?? )v
?? ?? ?? 
(2009 : 20 Marks) 
Solution: 
Let ?? be the equilibrium position of the body and ???? =?? . 
In position of equilibrium 
???? =2???? ·
?? ?? ??? =
?? 2
 
When particle is dropped from ?? it free falls till ?? . 
?? ?? =0+2?? ×???? 
? ?? ?? =v2???? 
 
After ?? the tension in the string starts acting which is balanced at ?? . Beyond ?? the 
particles moves due to its velocity till it comes to stop at ?? . 
At any point ?? with ???? =?? . 
Page 2


Edurev123 
Dynamics & Statics 
1. Rectilinear Motion 
1.1 One end of a light elastic string of natural length ?? and modulus of elasticity 
?????? is attached to a fixed point ?? and the other end to a particle of mass ?? . The 
particle initially held at rest at ?? is bit fall. Find the greatest extension of the string 
during motion and show that the particle will reach ?? again after a time. 
(?? +?? -?????? -?? ?? )v
?? ?? ?? 
(2009 : 20 Marks) 
Solution: 
Let ?? be the equilibrium position of the body and ???? =?? . 
In position of equilibrium 
???? =2???? ·
?? ?? ??? =
?? 2
 
When particle is dropped from ?? it free falls till ?? . 
?? ?? =0+2?? ×???? 
? ?? ?? =v2???? 
 
After ?? the tension in the string starts acting which is balanced at ?? . Beyond ?? the 
particles moves due to its velocity till it comes to stop at ?? . 
At any point ?? with ???? =?? . 
?? ?? 2
?? ?? ?? 2
 =???? -(2???? )
?? +?? ?? =-2????
?? ?? ? 
?? 2
?? ?? ?? 2
 =-
2?? ?? ?? 
So, the body performs SHM with centre ?? . 
Multiplying with 2
????
????
 and integrating 
(
?? ?? ????
)
2
 =-
2?? ?? ?? 2
+??    ???? ?? ,                                     ?? ?? =v2???? ,?? =-
?? 2
2???? =-
2?? ?? ?? 2
4
+?? ??? =
5
2
????
 
?                                                                           (
????
????
)
2
=
5
2
???? -
2?? ?? ?? 2
                                    (??) 
At ?? , 
????
????
=0
 
?                                                 ?? 2
=
5
4
?? 2
??? =
v5
2
?? 
So greatest distance through which particle falls 
 =???? =???? +???? +????
 =?? +
?? 2
+
v5?? 2
=
(3+v5)?? 2
 
Greatest extension =
(1+v5)?? 2
 
From (i), 
????
????
=
v
2?? ?? [
5
4
?? 2
-?? 2
]
1/2
 
where positive sign is taken as particle is moving in direction of increasing ?? . 
v
?? 2?? ????
v
5
4
?? 2
-?? 2
=???? 
Page 3


Edurev123 
Dynamics & Statics 
1. Rectilinear Motion 
1.1 One end of a light elastic string of natural length ?? and modulus of elasticity 
?????? is attached to a fixed point ?? and the other end to a particle of mass ?? . The 
particle initially held at rest at ?? is bit fall. Find the greatest extension of the string 
during motion and show that the particle will reach ?? again after a time. 
(?? +?? -?????? -?? ?? )v
?? ?? ?? 
(2009 : 20 Marks) 
Solution: 
Let ?? be the equilibrium position of the body and ???? =?? . 
In position of equilibrium 
???? =2???? ·
?? ?? ??? =
?? 2
 
When particle is dropped from ?? it free falls till ?? . 
?? ?? =0+2?? ×???? 
? ?? ?? =v2???? 
 
After ?? the tension in the string starts acting which is balanced at ?? . Beyond ?? the 
particles moves due to its velocity till it comes to stop at ?? . 
At any point ?? with ???? =?? . 
?? ?? 2
?? ?? ?? 2
 =???? -(2???? )
?? +?? ?? =-2????
?? ?? ? 
?? 2
?? ?? ?? 2
 =-
2?? ?? ?? 
So, the body performs SHM with centre ?? . 
Multiplying with 2
????
????
 and integrating 
(
?? ?? ????
)
2
 =-
2?? ?? ?? 2
+??    ???? ?? ,                                     ?? ?? =v2???? ,?? =-
?? 2
2???? =-
2?? ?? ?? 2
4
+?? ??? =
5
2
????
 
?                                                                           (
????
????
)
2
=
5
2
???? -
2?? ?? ?? 2
                                    (??) 
At ?? , 
????
????
=0
 
?                                                 ?? 2
=
5
4
?? 2
??? =
v5
2
?? 
So greatest distance through which particle falls 
 =???? =???? +???? +????
 =?? +
?? 2
+
v5?? 2
=
(3+v5)?? 2
 
Greatest extension =
(1+v5)?? 2
 
From (i), 
????
????
=
v
2?? ?? [
5
4
?? 2
-?? 2
]
1/2
 
where positive sign is taken as particle is moving in direction of increasing ?? . 
v
?? 2?? ????
v
5
4
?? 2
-?? 2
=???? 
If ?? 1
 is time from ?? to ?? 
v
?? 2?? ? ?
v5//2
-?? /2
?
????
v
5
4
?? 2
-?? 2
 =??
?? 0
?????
? v
?? 2?? [sin
-1
 
?? v5??/2
]
-?? /2
v5//2
 =?? 1
?? 1
 =v
?? 2?? [
?? 2
-sin
-1
-
1
v5
]=v
?? 2?? [
?? 2
+sin 
1
v5
]
 =v
?? 2?? [
?? 2
+tan
-1
 
1
2
]
 =v
?? 2?? [
?? 2
+
?? 2
-tan
-1
 2]
 =v
?? 2?? [?? -tan
-1
 2]
 
Time in falling from ?? to ?? 
1
2
?? ?? 2
2
=?? ??? 2
=v
2?? ?? 
? Total time taken to come back to 
?? =2v
?? 2?? [?? -tan
-1
 2+2]
 =v
2?? ?? [?? +2-tan
-1
 2]
 
1.2 The velocity of a train increases from 0 to ?? at a constant acceleration ?? ?? , then 
remains constant for an interval and again decreases to 0 at a constant 
retardation ?? ?? . If the total cistance described is ?? ?? find the total time taken. 
(2011 : 10 Marks) 
Solution: 
(i) When velocity increases from 0 to ?? . Using ?? =?? +???? ,?? =?? ,?? =0,?? =?? ?? ,?? =?? 1
, we 
get, 
                                          ?? =0+?? 1
?? 1
 
Page 4


Edurev123 
Dynamics & Statics 
1. Rectilinear Motion 
1.1 One end of a light elastic string of natural length ?? and modulus of elasticity 
?????? is attached to a fixed point ?? and the other end to a particle of mass ?? . The 
particle initially held at rest at ?? is bit fall. Find the greatest extension of the string 
during motion and show that the particle will reach ?? again after a time. 
(?? +?? -?????? -?? ?? )v
?? ?? ?? 
(2009 : 20 Marks) 
Solution: 
Let ?? be the equilibrium position of the body and ???? =?? . 
In position of equilibrium 
???? =2???? ·
?? ?? ??? =
?? 2
 
When particle is dropped from ?? it free falls till ?? . 
?? ?? =0+2?? ×???? 
? ?? ?? =v2???? 
 
After ?? the tension in the string starts acting which is balanced at ?? . Beyond ?? the 
particles moves due to its velocity till it comes to stop at ?? . 
At any point ?? with ???? =?? . 
?? ?? 2
?? ?? ?? 2
 =???? -(2???? )
?? +?? ?? =-2????
?? ?? ? 
?? 2
?? ?? ?? 2
 =-
2?? ?? ?? 
So, the body performs SHM with centre ?? . 
Multiplying with 2
????
????
 and integrating 
(
?? ?? ????
)
2
 =-
2?? ?? ?? 2
+??    ???? ?? ,                                     ?? ?? =v2???? ,?? =-
?? 2
2???? =-
2?? ?? ?? 2
4
+?? ??? =
5
2
????
 
?                                                                           (
????
????
)
2
=
5
2
???? -
2?? ?? ?? 2
                                    (??) 
At ?? , 
????
????
=0
 
?                                                 ?? 2
=
5
4
?? 2
??? =
v5
2
?? 
So greatest distance through which particle falls 
 =???? =???? +???? +????
 =?? +
?? 2
+
v5?? 2
=
(3+v5)?? 2
 
Greatest extension =
(1+v5)?? 2
 
From (i), 
????
????
=
v
2?? ?? [
5
4
?? 2
-?? 2
]
1/2
 
where positive sign is taken as particle is moving in direction of increasing ?? . 
v
?? 2?? ????
v
5
4
?? 2
-?? 2
=???? 
If ?? 1
 is time from ?? to ?? 
v
?? 2?? ? ?
v5//2
-?? /2
?
????
v
5
4
?? 2
-?? 2
 =??
?? 0
?????
? v
?? 2?? [sin
-1
 
?? v5??/2
]
-?? /2
v5//2
 =?? 1
?? 1
 =v
?? 2?? [
?? 2
-sin
-1
-
1
v5
]=v
?? 2?? [
?? 2
+sin 
1
v5
]
 =v
?? 2?? [
?? 2
+tan
-1
 
1
2
]
 =v
?? 2?? [
?? 2
+
?? 2
-tan
-1
 2]
 =v
?? 2?? [?? -tan
-1
 2]
 
Time in falling from ?? to ?? 
1
2
?? ?? 2
2
=?? ??? 2
=v
2?? ?? 
? Total time taken to come back to 
?? =2v
?? 2?? [?? -tan
-1
 2+2]
 =v
2?? ?? [?? +2-tan
-1
 2]
 
1.2 The velocity of a train increases from 0 to ?? at a constant acceleration ?? ?? , then 
remains constant for an interval and again decreases to 0 at a constant 
retardation ?? ?? . If the total cistance described is ?? ?? find the total time taken. 
(2011 : 10 Marks) 
Solution: 
(i) When velocity increases from 0 to ?? . Using ?? =?? +???? ,?? =?? ,?? =0,?? =?? ?? ,?? =?? 1
, we 
get, 
                                          ?? =0+?? 1
?? 1
 
?                                 ?? 1
=
?? ?? 1
. 
Using                          ?? =???? +
1
2
?? ?? 2
 
We get, 
?? 1
 =0+
?? 2
·?? 1
·?? 1
2
 =
1
2
·?? 1
·
?? 2
?? 1
2
=
?? 2
2?? 1
 
(ii) When velocity decreases from ?? to 0 . Using ?? =?? +?? ?? 3
?? =0,?? =?? ,?? =-?? 2
,?? =?? 2
, 
we get,                                          0=?? -?? 2
?? 2
 
?                                                    ?? 2
=
?? ?? 2
 
Using 
?? =???? +
1
2
?? ?? 1
2
?? 2
 =?? ?? 2
-
1
2
·?? 2
?? 2
2
 =
?? 2
?? 2
-
1
2
?? 2
?? 2
=
?? 2
2?? 2
 
(iii) Since the total distance travelled is ' ?? ', the distance travelled during the constant 
velocity phase 
=?? -
?? 2
2?? 1
-
?? 2
2?? 2
 
Time taken to travel this distance, ?? 3
 
=
?? -
?? 2
2?? 1
-
?? 2
2?? 2
?? 
                                                                        =
?? ?? -
?? 2?? 1
-
?? 2?? 2
 
?                               Total time taken =?? 1
+?? 2
+?? 3
 
           =
?? ?? 1
+
?? ?? 2
+
?? ?? -
?? 2?? 1
-
?? 2?? 2
 
=
?? ?? +
?? 2?? 1
+
?? 2?? 2
 
Page 5


Edurev123 
Dynamics & Statics 
1. Rectilinear Motion 
1.1 One end of a light elastic string of natural length ?? and modulus of elasticity 
?????? is attached to a fixed point ?? and the other end to a particle of mass ?? . The 
particle initially held at rest at ?? is bit fall. Find the greatest extension of the string 
during motion and show that the particle will reach ?? again after a time. 
(?? +?? -?????? -?? ?? )v
?? ?? ?? 
(2009 : 20 Marks) 
Solution: 
Let ?? be the equilibrium position of the body and ???? =?? . 
In position of equilibrium 
???? =2???? ·
?? ?? ??? =
?? 2
 
When particle is dropped from ?? it free falls till ?? . 
?? ?? =0+2?? ×???? 
? ?? ?? =v2???? 
 
After ?? the tension in the string starts acting which is balanced at ?? . Beyond ?? the 
particles moves due to its velocity till it comes to stop at ?? . 
At any point ?? with ???? =?? . 
?? ?? 2
?? ?? ?? 2
 =???? -(2???? )
?? +?? ?? =-2????
?? ?? ? 
?? 2
?? ?? ?? 2
 =-
2?? ?? ?? 
So, the body performs SHM with centre ?? . 
Multiplying with 2
????
????
 and integrating 
(
?? ?? ????
)
2
 =-
2?? ?? ?? 2
+??    ???? ?? ,                                     ?? ?? =v2???? ,?? =-
?? 2
2???? =-
2?? ?? ?? 2
4
+?? ??? =
5
2
????
 
?                                                                           (
????
????
)
2
=
5
2
???? -
2?? ?? ?? 2
                                    (??) 
At ?? , 
????
????
=0
 
?                                                 ?? 2
=
5
4
?? 2
??? =
v5
2
?? 
So greatest distance through which particle falls 
 =???? =???? +???? +????
 =?? +
?? 2
+
v5?? 2
=
(3+v5)?? 2
 
Greatest extension =
(1+v5)?? 2
 
From (i), 
????
????
=
v
2?? ?? [
5
4
?? 2
-?? 2
]
1/2
 
where positive sign is taken as particle is moving in direction of increasing ?? . 
v
?? 2?? ????
v
5
4
?? 2
-?? 2
=???? 
If ?? 1
 is time from ?? to ?? 
v
?? 2?? ? ?
v5//2
-?? /2
?
????
v
5
4
?? 2
-?? 2
 =??
?? 0
?????
? v
?? 2?? [sin
-1
 
?? v5??/2
]
-?? /2
v5//2
 =?? 1
?? 1
 =v
?? 2?? [
?? 2
-sin
-1
-
1
v5
]=v
?? 2?? [
?? 2
+sin 
1
v5
]
 =v
?? 2?? [
?? 2
+tan
-1
 
1
2
]
 =v
?? 2?? [
?? 2
+
?? 2
-tan
-1
 2]
 =v
?? 2?? [?? -tan
-1
 2]
 
Time in falling from ?? to ?? 
1
2
?? ?? 2
2
=?? ??? 2
=v
2?? ?? 
? Total time taken to come back to 
?? =2v
?? 2?? [?? -tan
-1
 2+2]
 =v
2?? ?? [?? +2-tan
-1
 2]
 
1.2 The velocity of a train increases from 0 to ?? at a constant acceleration ?? ?? , then 
remains constant for an interval and again decreases to 0 at a constant 
retardation ?? ?? . If the total cistance described is ?? ?? find the total time taken. 
(2011 : 10 Marks) 
Solution: 
(i) When velocity increases from 0 to ?? . Using ?? =?? +???? ,?? =?? ,?? =0,?? =?? ?? ,?? =?? 1
, we 
get, 
                                          ?? =0+?? 1
?? 1
 
?                                 ?? 1
=
?? ?? 1
. 
Using                          ?? =???? +
1
2
?? ?? 2
 
We get, 
?? 1
 =0+
?? 2
·?? 1
·?? 1
2
 =
1
2
·?? 1
·
?? 2
?? 1
2
=
?? 2
2?? 1
 
(ii) When velocity decreases from ?? to 0 . Using ?? =?? +?? ?? 3
?? =0,?? =?? ,?? =-?? 2
,?? =?? 2
, 
we get,                                          0=?? -?? 2
?? 2
 
?                                                    ?? 2
=
?? ?? 2
 
Using 
?? =???? +
1
2
?? ?? 1
2
?? 2
 =?? ?? 2
-
1
2
·?? 2
?? 2
2
 =
?? 2
?? 2
-
1
2
?? 2
?? 2
=
?? 2
2?? 2
 
(iii) Since the total distance travelled is ' ?? ', the distance travelled during the constant 
velocity phase 
=?? -
?? 2
2?? 1
-
?? 2
2?? 2
 
Time taken to travel this distance, ?? 3
 
=
?? -
?? 2
2?? 1
-
?? 2
2?? 2
?? 
                                                                        =
?? ?? -
?? 2?? 1
-
?? 2?? 2
 
?                               Total time taken =?? 1
+?? 2
+?? 3
 
           =
?? ?? 1
+
?? ?? 2
+
?? ?? -
?? 2?? 1
-
?? 2?? 2
 
=
?? ?? +
?? 2?? 1
+
?? 2?? 2
 
=
?? ?? +
?? 2
(
1
?? 1
+
1
?? 2
) 
1.3 A mass of ?????? ???? moving with a velocity of ?????? ?? /?????? strikes a fixed target 
and is brought to rest in 
?? ??????
 sec. Find the impulse of the biow on the target and 
assuming the resistance to be uniform throughout the time taken by the body in 
coming to rest, find the distance through which it penetrates. 
(2011: 20 Marks) 
Solution: 
Initial velocity,                           u=240 m/s 
Final velocity,                            v=0(as the mass finally comes to rest) 
Time taken to come to rest,    t=0.01s 
Using,                                         v=u+at, we get 
                                                    0=240+a*0.01 
?                                                    a=-24000m/?? 2
 
The negative sign indicates that the velocity of the bullet is decreasing. 
Using,                                         ?? 2
-?? 2
=2???? ,???? h??????   
                                                0-(240)
2
=2*?? *(-24000) 
? ?? =
-240×240
-2×24000
 =0.1 m
 
Hence, the distance of penetration of the mass into the fixed target is 0.1 m. 
impulse of the blow on the target, 
?? = Change in momentum of the mass 
 =???? -???? 4
 =?? (?? -4)=560×(-240)=-134400 kg m/s
 
1.4 (i) After a ball has been falling under gravity for 5 seconds it passes through a 
pane of glass and loses half its velocity. If it now reaches the ground in 1 second, 
find the height of glass above the ground. 
(2011 : 10 Marks) 
Read More
387 videos|203 docs

Top Courses for UPSC

387 videos|203 docs
Download as PDF
Explore Courses for UPSC exam

Top Courses for UPSC

Signup for Free!
Signup to see your scores go up within 7 days! Learn & Practice with 1000+ FREE Notes, Videos & Tests.
10M+ students study on EduRev
Related Searches

mock tests for examination

,

Rectilinear Motion | Mathematics Optional Notes for UPSC

,

video lectures

,

Free

,

past year papers

,

Semester Notes

,

Previous Year Questions with Solutions

,

Summary

,

Rectilinear Motion | Mathematics Optional Notes for UPSC

,

pdf

,

practice quizzes

,

Objective type Questions

,

Extra Questions

,

Important questions

,

Exam

,

shortcuts and tricks

,

Rectilinear Motion | Mathematics Optional Notes for UPSC

,

ppt

,

Sample Paper

,

MCQs

,

Viva Questions

,

study material

;