302 - Mechanics part 1 Questions Answers
Two cylinders are twisted by the same external torque.If the ratios of their modulous of rigidity , radii & lengths are 1:2, 2:3 & 3:4 respectively. Then find the ratio of angle of twist ??
Let the angle rotated due to torque = θ and angle of twist (shear) = δ
then arc covered = rθ (here r is radius)
now for twist of wire δ = rθ/l (here l is length)
according to formula η = F/Aδ and torque ζ = kFr (here k is constant of proportion)
we get ζ = kηAδr
Use the formula and get the answer, you have to calculate ratio of δ's so k is not required
A body is moving towards north with initial velocity of 13m/s. Its is subjected to a retardation of 2 m/s2 towards south.The distance travelled in 7th sec is ??
displacement of any particular sec. = u+at-(a/2)
here direction of motion is opposite to the direction of acceleration so formula will be u-at+(a/2)
displacement in 7th sec = 0
now we know that direction of motion will become south after 6.5 sec. so distance for last half sec = ut+(1/2)at2 = 1/4
same will be the distance for the first half sec of 7th. so total distance for 7th sec = 1/4 + 1/4 = 1/2