68 - Rotational mechanics Questions Answers
A simple pendulum of mass and length L is held in horizontal position. If it is released from this position, then find the angular momentum of the bob about the point of suspension when it is vertically below the point of suspension.
by energy conservation v = √(2gL) below the point of suspension
so angular momentum = mvL about the point of suspension
A rod of length L and mass m is free to rotate about its one end in vertical plane. If it is released from horizontal position, then find torque on rod about end of rotation , when it makes an angle θ with vertical line
force is mg and perpendicular distance from axis l/2 sinθ
now calculate
Four solid rigid balls each of mass m and radius r are fixed on a rigid ring of radius 2r and mass 2m.The system is whirled about ‘O’. The radius of gyration of the system is 128 mr2/30. How???
about O
M. I. of ring = 2m(2r)2
M. I. of one ball = 2mr2/5 + m(2r)2 = 22mr2/5
so total = 8mr2 + 4*22mr2/5
solve
One other thing is that the question is wrong, in the place of radius of gyration, you should write moment of inertia
what is projectile motion?
A particle thrown in such a way that velocity and acceleration makes variable angle with each other.
In some cases angle can be fixed
the reduced mass of two particle having masses m and 2m is 2m/m.how????.....
formula for finding reduced mass will be [m1m2/m1+m2]
A wheel starting from rest is uniformly accelerated at 2 radsec^2 for 20s.It is allowed to rotate uniformly for next 10s and finaly brought to rest in next 20s.Find total angle rotated by wheel ( in radian).
ω = 0 + 2(20) = 40 (according to rotational equation ω = ω0 + αt)
and θ = 0 + 1/2(2)(20)2 = 400 radian
in middle uniform part angle rotated = 40*10 = 400 radian
and since acceleration in first part and retardation in last part are equal so angle rotated in last part = 400 radian
total = 1200 radian
A body rotating with uniform angular acceleration covers 100 π (radian) in the first 5 s after the start. Its angular speed at the end of 5 s ( in radian/s) is
initial angular velocity = 0
so use θ = 1/2 αt2
and ω = αt
if A + B + C = 0 then A x B is
It is not given that in which terms we have to get answer so many answers are possible
A possible solution
A + B + C = 0
A+B = -C
B X (A+B) = - B X C
BXA + 0 = - B X C
AXB = BXC ( ANS)
This answer is given by SARIKA and modified by admin only.
my previous questn from rotational topic is still uncleared . I want to know why w= 4π is used.
according to rotational mechanics angular velocity = 2πn here n is frequency and in the problem n = 120 rotation/min = 2 rotation/sec.
from rest a body rotate 120rot/min for 20 sec then rotate for 5 sec with same rotation . find how many rotation it will make?
here while calculating ang. acc you use w= w0 + at , how w=4π , ( i want to know how to convert 120 rot/min)
120 rotation per minute = 120/60 = 2 rotation per second