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that mean x=3/4the distance of block from the level of head of the man is 18m and when to level the head with the block man travels 9m upwards and block 9m downwards.
tension acts towards the pulley and the weight acts opposite to tension i.e downwards.
force acting in the direction of acceleration is considered more in magnitude than the force in opposite direction
for the man
T-80g=80a equation 1
120g-T=120a equation2
adding both equations we get
40g=200a
a=0.2g (given g as 10ms^-2)
a=2ms^-2
v^2=2as (as initial velocity of both the objects is zero )
v^2=2*2*9
v^2=36
v=6ms^-1
for question 24
stress=F/A
F=stress*A
F=(stress/4)*4A (area would be 4A as (2D)^2 is four times greater than (d)^2 for e.g (2*2)^2=16 x(2)^2=4 see
stress should be divided by 4 as the examiner states that load is the same which means the force applied is the same
so to get F 4 must be divided by 4 to get 1 ok!!
stress is directly proportional to strain
so if stress is stress/4 .strain would also be strain/4
stress/4=x/3l.
stress=x/l main formula
coefficient of x would be such that it equals 3/4 because only then we would get our formula u see coefficients will change but the formula wont ok