As the block is held stationary
T + VV(g + a) = ρV(g + a)
T=−m ga+=×××
×()(). =
.
ρσ N
σ0510 212
05 10
24
3(^3)
(ii) If the thread snaps, T = 0.
Fnet = Fup – W = (ρ – V)V (g + a)
=××
×
0510 2 ×=
05 10
.^331224
.
N
acceleration of sphere =^24
2
= 12 ms−^2- (a) The knowledge of elasticity is applied in
designing a bridge such that it does not bend too much
or break under the load of traffic, the force of wind and
under its own weight. Consider a rectangular bar length
l, breadth b and thickness d supported at both ends, as
shown in figure. When a load W is suspended at its
middle, the bar gets depressed by an amount given by
δ= Wl
Ybd34 3Wdb l
d(b) Bending can be reduced by using a material with a
large Young's modulus Y. As G is proportional to d–3 and
to b–1, so depression can be decreased more effectively
by increasing the depth d rather than the breadth b. But
a deep bar has a tendency to bend under the weight of
a moving traffic, as shown in figure (b). This bending
is called buckling. Hence a better choice is to have a
bar of I-shaped cross-section, as shown in figure (c).
This section provides a large load bearing surface and
enough depth to prevent bending. Also, this shape
reduces the weight of the beam without sacrificing its
strength and hence reduces the cost.
b
d(c) I-shaped
cross-section of bar(b) Buckling of
a deep bar(a) Rectangular
cross-section of barJoint Entrance Examination
(Main) 2019
T
he JEE (Main)-2019 will be conducted by National Testing Agency
(NTA) twice before admissions in the next academic session. The
NTA will conduct the first JEE (Main)-January 2019 for admission to
Undergraduate Programs in NITs, IIITs and other Centrally Funded
Technical Institutions etc. on the weekends (Saturdays / Sundays) during
6 th January 2019 - 20 th January 2019. The test details are
given below:
Paper Subjects Mode of
ExaminationTiming of
Examination
First
ShiftSecond
Shift
Paper-1
(For B.E./B.
Tech.)Mathematics,
Physics &
Chemistry“Computer Based
Test (CBT)” mode
only09.30
a.m. to
12.30
p.m.02.30
p.m. to
05.30
p.m.
Paper - 2
(For B. Arch/
B.Planning)
(to be
attempted
in one
sitting)Mathematics
Part I
Aptitude Test
Part II“Computer Based
Test (CBT)” mode
only
Will be held in one
Drawing Test shift only
Part Ill“Pen & Paper
Based” (offline)
mode to be
attempted on
Drawing sheet
The exact date and shift allotted to candidates for JEE (Main) - January
2019 shall be displayed by the 5th October 2018 on the NTA websites
A candidate may appear in Paper 1 and/or Paper 2 depending upon
the course/s he/she wishes to pursue. All the candidates aspiring to take
admission to the undergraduate programs at IITs for the year 2019 will
have to appear in the Paper-1 (B. E. /B. Tech.) of JEE (Main)-2019. Based on
the performance in Paper-1 (B. E. /B. Tech.) of JEE (Main)-2019, a number
of top candidates as per the requirement of JEE (Advanced) (including all
categories) will be eligible to appear in JEE (Advanced)-2019.
Similarly, the second JEE (Main) - April 2019 will be conducted between
6 th April 2019 - 20 th April 2019 for which a separate notice will
be issued later on and the candidates will be required to apply separately.
However, candidates are not required to compulsorily appear in both the
tests i.e. JEE (Main) - January 2019 and JEE (Main) - April 2019. In case,
a candidate appears in both the tests, the better of the two scores will be
used for the admissions and eligibility for JEE (Advanced)-2019.
Candidates who desire to appear in the JEE (Main) - January 2019
may see the detailed Information Bulletin for JEE (Main) -
January 2019 which is available on the website http://www.nta.ac.in and
http://www.jeemain.nic.in w.e.f. 1 st September 2018.