2018-10-01_Physics_For_You

6. (d) : For small displacement, y
   = x
   sinθ
   2 kx 0 sinq = mg ...(i)
   If ring is displaced y
   mg – 2k(x 0 + y sin q)sin q = ma

a k

m

=−^2 y

sin^2 θ

...(ii)

On comparing with the

standard equation

a = –Z^2 y

ω^2 θ

2 2

= k

m

sin

T m

k

= 2

2 2

π

sin θ

7. (d) : Velocity of a particle in S.H.M. is given by

vA=−ω^22 x

Taking square on both the sides

v^2 = Z^2 (A^2 – x^2 ) = 3Z^2 a^2 ⇒=ω = −

v

3 a

1 rads^1

x = 2a sin(Zt + φ)on differentiation with respect to t

v = dx

dt

= 2aZ cos(Zt + φ)

1

2

=sinφ⇒=φπnn+−() 11 nnαπ=+()− π

6

vvatφ==π +=veandatvφ π=−e

6

5

6

So,φ=π

6

x = 2a sin(Zt + φ) = 2a[sin Zt cos φ + cos Zt sin φ]

=+











(^2) 

3

2

1

2

atsincωωos t^ (Z = 1 rad s–1)

xa=+(s 3 inttcos)

8. (c) : ggeff= 5.

erefore pressure at centre

=+PR 0 5 ρ g

9. (c) : When a spherical object of radius r moving at
   velocity v through a uid of viscosity coecient K
   will experience a viscous force F given by
   F = 6pKrv
   ma = 6pKrv

m dv
dt

− rv







= 6 πη

−mdv=

v

6 πηrd. t

q q

y

yq

x

2 g

2 g P 0

Ö 5 g g

Taking integration on both the sides

−=∫∫dv

v

rdt

t

2

05

0

6

.

πη

−=∫∫dv  

v

dt

t

2

05

0

6 1

18

.

π

π

−=⇒− 







[ln]v 205. ttln. =

3

05

23

ln

.

(^2) ln s
05 3
=⇒t t= 34

10. (b) : v = velocity of rod, e = Blv
    q = C × V
    Now, q = C × Blv
    (Where q is the amount of charged stored in a
    capacitor)

i

dq

dt

d

dt

==()BlvC

dv

dt

 =a

= CBla

? mg – ilB = ma

mg – (CBla)lB = ma ; (^) a mg
mCBl

=

+^22

CBSE board question paper pattern to change from 2020

A

ccording to media reports, CBSE is planning to make some changes

in the examination pattern of class 10 and class 12 from 2020 as

part of a revamp that would include changes in the examination schedule

for vocational subjects as well as for the main subjects - among other

changes. Citing MHRD sources, it is reported that the initiative of this

pattern change is being taken to discourage students from rote learning.

The new pattern would test students on their analytical skills and

reasoning abilities instead of blind copy pasting of textbook text. The

board has also claimed that this step will produce a better result and the

academic quality of institutions will be renewed

Following are some of the major changes expected to be introduced in the

new CBSE exam pattern 2020

Ø Question papers to be designed to check the problem-solving and

analytical thinking of students

Ø Paper pattern to be revamped to include more short answer-type

questions like those ranging from 1 to 5 marks

Ø Vocational course exams to be held in February, and the final board

exams to conclude by March in around 15 days.

Ø Following the early wrapping up of boards, the results are likely to be

declared earlier than the schedule followed in the current structure.

This will give evaluators more time to check papers. Results, too, will

likely be declared earlier.

Under the new plan, there is a vision for putting more emphasis on

improved quality of academics in institutions such as teachers, learning

outcomes and pedagogy. Respective state governments would be

responsible for evaluating their schools’ working criteria, infrastructure,

and facilities, and their report will be the guide for CBSE to arrive at a

decision. CBSE’s renewed paper pattern also aims to simplify and shorten

the rules of affiliation and renewal for schools.