114 - Kinematics Questions Answers
a particle is moving along a straight line such that its position varies with time t as x=6α [ t+ αsin (t/α)
where x is its position in metre, t is time in s and α is a positive constant
The particle comes to rest at time t = (in terms of α and π)
differentiating given x w. r. t. t
dx/dt will be v
for rest v = 0
a vector a which has magnitude 8 is added to a vector B which lies on x-axis. The sum of these two vectors, lies on y-axis and has a magnitude twice of the magnitude of B. The magnitude of vector B is
let a = 8cosAi+8sinAj and B = bi
sum of the two = 8cosAi+8sinAj+bi
it is given as 2bj
so 8cosAi+8sinAj+bi = 2bj
so (8cosA+b)i+8sinAj = 2bj
now on comparing coefficient of i and j we get
cosA = -b/8 and sinA = 2b/8
now use sin2A +cos2A = 1
the forces F1 and F2 are acting perpendicular to each other at a point and have resultant R. If force F2 is replaced by R2 - F12/F2 acting in the direction opposite to that of F2, the magnitude of resultant
F12 + F22 = R2 (1)
now for second condition
F12 + [(R2 - F12)/F2]2 = R12 R1 is new resultant
on putting the value of R2 from first eq. we get
F12 + [ F22/F2]2 = R12
so R = R1
A sleeping cat and a sleeping dog are initially at a distance 'l' metres. As soon as the dog wakes up, the cat runs in the horizontal direction with constant velocity of u m/s. Immediately the dog chases the cat with constant speed of v m/s. Initially the dog was facing the north direction towards cat. The cat starts running in the east direction. Assuming the dog aims at the cat with constant speed v m/s, find the time after which the dog chases the cat.
see video for this solution in you tube by the name iitbrain.com
video: i e irodov 1.13
Time of flight of a projectile thrown from ground is 8√5 s. It will rise up to a height of.........
T = 2usinθ/g
by formula calculate usinθ
then put in H formula
A projectile is projected with velocity u= ai+bj from ground if acceleration due ti gravity is g, then the change in velocity of the projectile in second of projection is
for t sec of projection v = u + at so v = ai+bj-gtj
now calculate v-u then mod
A shell at rest at large height explodes into two parts which move horizontally with speeds v1 and v2. After what time their instantaneous velocities are perpendicular?
please see iitbrain video for the answer in you tube
iitbrain.com in you tube
video name i e irodov problem 1.11
A particle moving in uniform circular motion undergoes an angular displacement α (less then 360°) from point P and Q. Then angle between average velocity from P to Q and velocity at Q is........
as clear from the figure that angle is a/2
A particle moves in the plane xy with velocity v = ai + bxj, where i and j are the unit vectors of the x and y axes, and a and b are constants. At the initial moment of time the particle was located at the point x = y = 0. Find:
(a) the equation of the particle's trajectory y(x);
(b) the curvature radius of trajectory as a function of x.
see the video in you tube by the name iitbrain.com
video i e irodov 1.35
A ball is thrown up with some velocity after time t second it is at height h from the ground which is given by h = at -1/2 bt2. The dh/dt is zero at t equal to
dh/dt = a - bt
so for dh/dt = 0
t = a/b