IIT JEE , AIEEE Forum - Physics , Mechanics

sachin_gupta1991

Someone plzz help me with problem 23 and 28 of class 11 hc verma,newtons laws, on page 80 and 81.

23) consider the atwood machine...................................

28)Let m₁₌1 kg , m₂= 2kg ,m₃= 3kg ..............................

SALUTES ASSURED FOR ALL ACCEPTABLE ANSWERS.

sachin_gupta1991

plzzzz reply, goiitians. I have a test tomorrow.Help me!!!!

astronautameya

hey sachin........... the 23d is a really wonderful question.
wat u have to do is, find the velocities of the 2 masses after2s.
now, the velocity of larger mass becomes 0 and the smaller is like projected upwards with some velocity.
at the point when the larger mass is stopped, let length of rope on left and right be x and y respectively.
now, if t is the time 2 becum taut again, then the smaller mass moves d1= ut-1/2 g. t^2 and the larger d2= 1/2 g t^2
so, the length on string on left at the end of that time t is x - d1 that on the right is y+d2.

now the string is inextensible, so the sum of these above terms = x+y

solve 2 get answer

Omi

see sachin....its a good question....wat u do first is tke out the accelarations if the bodies....needless to say we hv an advantage here coz this is the simplest profile u ll get... acc of one body= - acc of the other one....isnt it....this is ur constraint eq.... nw frm the fbds of both the bodies.... take out equations.... solve n gt the respective accelerations......nw use kinematics to gt the first answer.....

biki

m1= mass on LHS of pulley = 300 g
m2 = mass on RHS of pulley = 600 g
let T = tension and a = accl^n of the system
force equ^s are----->>>
T - 300g = 300a
600g - T = 600a
Solving for a ..... we get a = g/3
So the system moves with accl^n = g/3 and string is tight now.
Now after 2 s of starting of motion the larger mass is stopped.
velocity at end of 2 second is u + at = g/3 x 2 = (2g/3) [as u = 0]
Now if this velocity is again acquired by the second block, the string will become tight again....
while falling now...(as the string is slack)....the body falls with accl^n 'g' after starting from rest again.
So 2g/3 = 0 + gt
or t = 2/3 s

biki

for problem 28 sol^n ....
refer to the problem 9 in page 74 of HCV - 1

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