IIT JEE , AIEEE Forum - Physics , Mechanics

uday_zingtudor

Answers for questions from DC pandey

1) The metre stick is just given a gentle push.That implies no velocity has been imparted to it horizontally.

Initially the centre of mass is at a position '0' on the x-axis.Now the
rod which is held vertically falls down.The centre of mass shifts down due to change in vertical position.

So the horizontal position of centre of mass is not shifted

The upper end wud be at +0.5 and the lower one at -0.5

6)It's just conservation of momentum!!

mv1/4 = 3mv2/4

for the position u just multiply by time and resolve into components.But that isn't required here.U can directly get the answer as y= -5cm

7) This one is damn easy!!

Just take care of the centre of mass.

Let mass of boat be at '0' and, A at -2 and B at +2

Locate the position of centre of mass!!

Thatz x= -2(50)+0(40)+2(60)
50+40+60

x=13cm

When the persons move closer the centre of mass remains in the same position and the boat moves by 13cm.

15)You have to be cool while u imagine the situation!!

The first ball strikes the other traveling a distance piR in 4s

That implies its velocity is piR/4

Coefficent of restitution = vel of separation/vel of approach

And that implies velocity of seperation is piR/20

applying CO momentum vel of each ball is piR/40 and they strike again after traveling a distance piR

The time taken wud be 40 seconds

~Cheerioi!!

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