303 - Mechanics part 1 Questions Answers
Why earth moves in orbital motion around the sun ...? why not in circular motion...?
Since every heavenly body like sun, earth, moon are rotating freely in free space, there is no body which is placed on a base, so rotation of every body depends on all the surrounding bodies. It means its track will also depend on the attraction forces given by all the surrounding bodies.
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