S1B - 2022

Sunday, July 31, 2011

Entrance Question Answers: Motion in Stright line

Q1.
Water drops from the roof of a building 10 m high. The drops fall at regular intervals of time, the first drop striking the floor at the instant the 4th drop begins to fall. Find positions of individual drops,when a drop strikes the floor?


Let t is the time interval between A,B,C and D positions
That means, 3t second taken to travel from A to D.
That is, 10 m traveled in 3t seconds.

S = ut + 1/2 a t^2 

10 = 0 + 1/2 x 10 (3t)^2

10 = 5 x 9 x t^2

t^2 = 2/9




 Now,  

S1 = ut + 1/2 g t^2 

S1 = 0 + 1/2 x 10 x  2/9 = 10/9 m (AB length)

 S1 +S2 = 0+1/2x10x(2t)^2
 S1 +S2 = 0+1/2x10x(2x2/9)^2 = 40/9 m (AC length)

S1+S2+S3 = 0+1/2x10x(3t)^2
S1+S2+S3 = 0+1/2x10x(32/9)^2 = 10m  (AD length)