Effects of Forces - s22 qp 11 -qn - 13 qp 12 qn 8

 


answer is A x and y are distances.
R * y = P * x this is equilibrium condition 
y decreases and therefore force at P should decrease. as P decreases, the force at Q should decrease to keep the rod equilibrium. 

the answer is A 
the child pulls the rope with a force of 12 and the tension in the rope pulls the child and sledge system. 
making two equations for child and sledge system and child. 
for child, 12 - Fr = ma 
for child and sledge system, 24 = ma 
24=  60 a , a = 0.4 
12- Fr = 20 * 0.4 : fr= 4 N 
you must be wondering from where do i get 24 N for the child and sledge system, 
you need to understand the double pulley system where the efforts gets doubled by using two pulley to lift the load. the same concept is applied here to add 12 + 12 = 24N.




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