IIT JEE , AIEEE Forum - Physics , Mechanics

amarswamy

hey goiitians i have got a good idea over here

well iam planning to help all my friends with shortcut formulae in all subjects

u can lend a hand too

all u have to do is to post any shortcut formulae for any concept and specifying the subject u can brief about its applications.

u can rate the formulae u liked the most

get ready frez lez start now

amarswamy

all viewers requested to p[ost a short cut trick here
rate the trick u liked the most and u can rate me too

varun.tinkle

copied from chinmanshu
here are some shortcuts to find ............... in motion in 1 dimension

1) to find the vel. in b/w the distance travelled

V1 = {v2 + (v2 - u2/n)}1/2

2) a bullet is fired with certain vel. into a block of wood . it loses 1/nth of its initial speed after travelling a dist. x in the block . determine the total dist. penetrated by it before coming to rest....
ans)
x' = {N2/ 2n - 1} x

where N is the amt of speed it loses (eg. if 1/10 th loses then N = 10)

NEVERTHLESS PLS RATE ME!!!!!!!!

joking

varun.tinkle

a vehicle of mass m travelling with vel. "v" stopped by applying const. braking force "f" within a dist. "x"

x/x * 100 = {(v2)2 - (v1)2 } / (v1)2 * 100

% dec in v1 = 20%
then % dec in x = 30%

if dec in v1 = 10%
then dec in x = 19%

if inc. in v1 = 10%
inc. in x = 21%..............................

varun.tinkle

vel of projectile at any instant

v = { u2 cos2 + ( u sin -gt)2}1/

varun.tinkle

least counts............

meter scle = 10-3 m
vernier caliper = 10-4m
screw gauge = 10-5m
wall clock = i sec.
stop clock = 1/100 sec.
spherometer = 1/100 mm

varun.tinkle

in projectiles...............

y = xtan$ {1 - x/R}

R = range............

varun.tinkle

for a projectile motion...............

R / H = 4 /tan $

varun.tinkle

for angle $ and pi - $ range is same u all know
but

T1 (for $) + T2 (for pi - $ ) = 2R/g

H1 (for $) + H2(for pi - $ ) = Hmax.

H1 . H2 = R^2/16

varun.tinkle

min. no. of equal vectorsthat can give zero resultant is 2
" " " un= " " " " " " " 3

and in case of unequal vectors all the three vectors must form a triangle

varun.tinkle

wo vectors give resultant = to either of them wen angle b/w them is 120 degress

mag. of vector addition = mag. of vector subtraction wen angle b/w them is 90 degrees

mag of dot product = mag. of cross product wen angle is 45 degress

varun.tinkle

projectile thrown parallel to hor.

T = {2H/g}^1/2

R =u (2H/g)^1/2

K.E of projectile at the top
K(top) = Kcos^2$

varun.tinkle

acceleration of a system of bodies.

a = force/ mass ....forces not including tension n normal reaction

eg.
2 masses attached on either sides of a massless pulley,
force = m1g - m2g ,
mass =m1 +m2
a= m1g - m2g/m1 +m2

also applicable in rotation,
a = force/ mass

in case of a pulley wid moment of inertia = I &radius r
mass of pulley is taken as I/r2

a = (m1g - m2g)/m1 +m2 + I/r2

varun.tinkle

2 masses attached at the ends of a spring, of stiffness = k

transform d case into a one mass & spring system,
spring constant(k) remains same; the massof the new block taken as

1/ = 1/m1 + 1/m2
or

=m1m2/m1 + m2

useful in solving shm, centre of mass & work, power energy probs.

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