JEE 2021 Solution Series | Work Energy Power | COM & Collision | JEE Physics #MissionJEE2025

In this series Mohit Sir provides chapter wise solution of Physics questions came in JEE Main 2021 in all attempts | JEE Main 2021 Physics solutions | JEE Main 2021 Complete Physics Solutions | Work Energy Power Solution of JEE Main 2021 | JEE Main 2021 Collision Solutions

Timestamp:
00:00 Introduction
00:14 List of Important Questions
00:23 Feb 2021 attempt Solution (WEP, COM & Collision)
19:43 March 2021 attempt Solutions (WEP, COM & Collision)
56:29 July 2021 attempt Solutions (WEP)
01:18:12 July 2021 attempt Solutions (COM & Collision)
01:30:31 Aug 2021 attempt Solutions (WEP)
01:40:36 Aug 2021 attempt Solutions (COM & Collision)

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[mohitgoenka]

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[dharampal]

Question 1 COM 1:08
Question 2 WPE 4:09 (P=√2mke)
Question 3 COM 5:32
Question 4 WPE 8:00
Question 5 VCM 8:43
Question 6 WPE 14:25
Question 7 COM 19:37
Question 8 Com 20:47
Question 9 WPE 22:00
Question 10 WPE 25:21
Question 11deadly 26:35
Question 12 WPE 36:54
Question 13 COM 41:11
Question 14 WPE 43:56
Question 15 COM 45:46
Question 16 WPE 47:45
Question 17 WPE 48:35
Question 18 com 50:41
Question 19. Wpe 52:50
Question 20 wpe 54:14

[SakshiSingh]

1:41:39, rocket que., good, F(upthrust)=V(relative)×dm/dt
1:50:17, good (METHOD OF CALCULATION)
1:53:15 fractional change in k.E.=(kf-ki)/ki👈

[sumantripathi]

feb
1) dependence on radius and mass, sigma=m/A 4:04
2) 5:07
3) collision com y direction most repeated 7:25
4) 8:39
5) 14:07
6) 15:58
7) 19:34

march
1) 21:55
2) 25:05
3) 26:12
4) e=coefficient of restitutuon 28:54 31:37 34:27 36:39
5) if not mention take e=1 40:36
6) semicircular disc=4a/3pie along y 43:38
7) by wet, w=k 45:26
8) 48:17
9) 48:17
10) 50:24 method 2 usinf equation ..a, then force
11) 52:39
12) 53:50
13)imp ** 56:21

july
1) 1:00:04
2) 1:01:20
3) most repeated 1:02:54
4) 1:04:54
5) 1:06:58
6) 1:08:08 1:09:33
7)1:12:20
8) 1:14:05
9) 1:17:16

july
1) 1:22:35
2) 1:23:16 1:24:15
3) 1:27:41
4) 1:30:28

august
1) tricky 1:33:24
2) op method 1:34:55
3) 1:37:00
4) 1:40:34

august
1) 1:42:49
2) 1:45:03
3) com then coe 1:50:22
4) 1:53:18
5) 1:55:49

[adityamehta]

FEB ATTEMPT

1.✅COM(CONCEPT MATCHED, READ QUESTION CAREFULLY)
2.✅WPE(KE=P^2/2M)
3.❌COM DEFLECTION AFTER COLLISION ( NET MOMENTUM IN Y DIRN SHOULD BE EQUAL)
4.✅WPE(P=ROOT 2MK)
5.❌VCM(T1-T2=6MG, NEED TO WRITE 2 EQNS)
6.✅WPE (F=-(dU/dR)
7.✅❌COLLISION (answer needed more manipulation, concept matched)

MARCH ATTEMPT

1.✅COLLISION ( MOMENTUM ALONG Y CONSERVED WHEN BALL DEFLECTED AT ANGLE)
2.❌COLLISION(FIRST FIND V THEN U IN MASS-BULLET SYSTEM)
3.❌WPE(CONCEPT MATCHED, PROCESS MATCHED, CALCULATION ERROR COMING, CHECK AGAIN)
4.❌COLLISION {VERY GOOD QUESTION} ( H1, H2 ETC. ARE 2*e2H1, T= ROOT 2H/G)
5.❌COLLISION(CONCEPT ERROR, WHEN NOTHING GIVEN IN QUESTION TAKE COLLLISION AS ELASTIC, THEN SIMPLY USE REDUCED MASS CONCEPT, SPEED OF SECOND BLOCK NOT TO BE TAKEN AS INITIAL(REST) )
6.✅COM (COM OF COMMON FIGURE)
7.❌WPE ( COMBINATION OF WET AND POWER)
8.✅ COLLISION(Pi=Pf ALONG Y DIRN)
9.✅ WPE (SIMPLE QS OF ENERGY CONSERVATION)
10.✅WPE (NORMAL APPLICATION OF WET)
11.✅ COLLISION( Pi=Pf APPLICATION, TAKE ELASTIC COLLISION WHEN UNMENTIONED)
12.✅ WPE(V^2=R -> HYPERBOLIC CURVE)
13.✅WPE(CONSERVATION OF ENERGY)

JULY ATTEMPT(WPE)

1.❌WPE(ENERGY CONSERVATION TO BE DONE SEPERATELY FOR SPRING AND NOT FOR POTENTIAL)
2.✅WPE(KE = P^2/2M)
3.✅WPE(PT=WORK DONE, W=CHANGE IN K)
4.✅WPE(SIMPLE CONCEPT OF WORK-ENERGY T)
5.✅WPE(SIMPLE QUESTION OF ENERGY CONSERVATION)
6.✅WPE(BASIC QUESTION OF WORK DONE -> INTEGRATION OF VARIABLE FORCE)
7.✅WPE (GRAPH QUES DO AGAIN)
8.❌WPE(PT=W -> DELTA K)
9.❌WPE(COMPONENT OF MG = CENTRIPETAL FORCE, N= 0) {NOTE: RECHECK FS H =2R/3 FORMULA)


JULY ATTEMPT(COM)

1.❌(USE MUZZLE VELOCITY DIRECTLY)
2.✅(STANDARD FORMULA FOR COM OF SEMI-CIRCULAR RING)
3.✅(MULTI CONCEPT QUE OF MOMENTUM CONSERVATION AND VELOCITY OF COM)
4.✅(SIMULTANEOUS USE OF COLLISION CONCEPT)

AUGUST ATTEMPT(WPE)
1.❌(GOOD QUESTION OF CHAIN HANGING, RETRY)
2.✅(RETRY WITH FORMULA = FCosx = const)
3.✅(Concept application of WET)
4.❌(Rare concept, good question)

AUGUST ATTEMPT(COM)
1.❌(MIXED QUESTION OF ROCKET PROPULSION + FORCE ANALYSIS)
2.✅(MIXED QUESTION OF MOMENTUM CONSERVATION + VCM)
3.❌(GOOD QUESTION WITH MATHEMATICAL MANIPULATION)
4.✅(RETRY, KE QUESTION CONCEPT APPLICATION)
5.✅(SAME AS Q5)

[sanvirathore]

Questions to revise:
March: 4, 5
July: 7, 9, 1
Aug: 1, 4, 3

[uchiihaa]

July COM 4Qs

Concepts to remember:

1. Muzzle speed is velocity of bullet wrt gun

3. Velocity of com is constant before and after collision as no ext. Force acting

4. During inelastic collision, both masses kinda combine and move with same velocity of both masses are same

[Sam_chatterjee]

SELF REFERENCE (WPE QUESTIONS):
4:09 easy
7:29 easy (K=p^2/2m)
8:53 revise(remmember relation)
14:16 easy(2020 pyq)
22:00 mixed concept(revise)
25:20 easy
36: 59 mixed concept
44:09 repeating concept(Pt=1/2mv^2)
47:52 easy
48:31 revise
52:51 graph
54:10 easy
57:20 good qs(revise)
1:00:15 easy
1:01:32 repeating concept(Pt=1/2mv^2)
1:03:30 easy
1:05:50 energy conservation
1:08:00 easy
1:09:50 concept based(revise)
1:12:34 repeating concept(Pt=1/2mv^2)
1:14:19 revise
1:31:47 revise(silly mistake)
1:33:47 easy
1:35:40 observation
1:37:55 revise

[anhad]

WPE ( GQS)
11:11 remember result
50:18 wet wala method ( u did by eqn of motion)
56:22 x nhi pucha hai l-x pucha hai
1:17:25 high chance of repeating in 2024 costheta=2/3
1:31:03 chain
1:38:31 revise
COM
27:53 RÉVISE
42:20
1:42:00 don't forget mg
1:47:53 repeat

[paridhikumari]

29:41 Retry e=Vsep/Vapproach
1:32:37 h~Reference level se C. O. M
1:37:22 Wagon's 10%energy converted to E. P.E
1:26:22 Ft(thrust force)= (Vrelative) (dm/dt)
Equation: Ft-mg=ma

[fahadshabbir]

4:06 M prop to r^2
7:26 intially momentum sirf x dirn me tha to final momentum bhi sirf x me hoga y dirn wala momentum zero hoga
19:31 easy but revise
20:02 same concept as 7min wala

MARCH ATTEMPT

1. COLLISION (MOMENTUM ALONG Y CONSERVED WHEN BALL DEFLECTED AT ANGLE)
25:00 2. COLLISION (FIRST FIND V THEN U IN MASS-BULLET

SYSTEM)

3 26:13 frictionless surface hai to rolling ni hoga translational motion hoga, to rolling k.E =0 hoga sirf translation k.E. hoga

4. 36:21 avg speed = total dist / total time remember
6 43:38 good ques revise concept again and remember com of semicircular disc 4R/3π
45:30 revise
50:29 kinematics se bhi kar sakte but ye aur energy conservation se easy hai
53:49
1:01:16 error wala formula small change ke liye hota
1:01:58 repeated concept w= power × t
1:04:46 easy but good
1:11:08 conservative force ke ko pe and vice versa me convert karta, energy ka loss ni hota, mechanical energy conserve rehta
1:17:53 normal zero when cosx = 2/3 remember for speed solving
1:20:04 muzzle vel = vel of bullet wrt gun hota hai. ( good ques must revise again) 1:24:18 remember concept for non uniform masss distribution.
1:27:23 during collision Vel of com const hota hai ke loss ho sakta lekin com ka vel constant rahega .
1:32:31 For continuous body change in P.E = mg×Hcom
1:37:00 isme galti kiye the
1:42:49 easy
1:50:05 very good ques must revise
1:55:12 easy but ek baar dekh lo

[Mynotes-mruw]

6:41 Collision me momentum is conserved and not only the magnitude but direction ka bhi dhyan rakhna hota hai
11:39 easy but phir se ek baar kro
15:00 condition for equilibrium
1:02:23. 1:13:58
1:07:29 work done by variable force

[aniketsinha]

Wep completed
#20 days block revision
Block 3 completed
Wep was easiest one in 2021 for me 😊
Only bcoz of you sir
Today I studied this chapter first tym
And I was thinking I will not able to do question by myself bcoz it's first tym
But sir I was able to solve 95 percent of questions
only through your concept vedios 🙏🙏🙏🙏

[sristibhuyan]

57:39 2 steps
1:05:16 go with loss in u = gain in KE
1:10:02 graphical
1:14:32 find v from equation of centripetal acc
1:32:34 redo
1:37:12 confused
32:00 tough

[georgey]

part 2; q2, 4, 5, 6,
part3; q4, 9
part4: q3
part5; q1
part6 q1, q2( never conserve KE unless specified perfectly elastic as it might be wrong, always momentum, q3, 4(KE can go beyond it's initial value)
If nothing said about collision, assume it is elastic e =1
While taking KE no need to consider velocity direction as KE is scalar

[anshika]

revision questions for wep and circular motion:
36:40, 43:42, 54:03, 55:12(length of compressed spring is not equal to just the compression), 1:03:50, 1:40:25

[sudhishvijai]

FOR MY REFERENCE
WPE
Q1 14:20 (EQUILIBRIUM F=0, dU/dx = 0)
Q2 44:00 ( x = t^3/2 rem!!)
Q3 53:00 ( r increase U increase therefore K.E decrease, v^2 = 1/r)
Q4 56:40 ( imp concept, apply tmect for only horizontal axis)
Q5 1:00:30 ( easy, rem 2 times = increase in 100%)
Q6 1:11:00 ( good understanding of U v/s x graph)
Q7 1:13:00 ( east but do again)
Q8 1:31:00 ( good question)
Q9 1:37:30 ( good question)

[kushalmohan]

com and collision
Aug
Q1 Fth= Vrel × dm/dt
F=Fth -mg

Q2 bob to describe or complete circle is v=√5gL

Q3 ratio m/M revise it

Q4 if a body split into equal part then take body mass 2m

Q5 same as q4

July attempt
Q1 muzzle speed is that velocity of bullet with respect to gun
Q2 com semi circular ring =2R/π
Q3 elastic e=1 then find vcom
💥Q4 same as q3

[Piyush-mkft]

Revision to do: (only WEP)
Feb :
Q5
March :
Q7
Q12
July :
Q 1
Q4
Q5 (must...why 1/2mu² - 1/2mv²...jbki ∆K =Kf -Ki)
Q7
Q9 (most imp)
August :
Q1
Q4 (must)

[uchiihaa]

Wep Aug 4Qs
Q3. Notice options only one is -ve (can be solved through options)

COM Aug 5Qs

Q3 ** good question
(Learning: Energy conservation may use in elastic collision if needed)