Question

the boy of mass 30 kg is at r1= 2 meters from the fulcrum. Of the girl is 45 kg, at what r2 must she sit so that they are balanced ?

Answer 1

here we need to balance the torque due to weight of boy with the torque due to weight of girl on the other side

so here we can say

(weight of boy) x (his distance from fulcrum) = (weight of girl) x (her distance from fulcrum)

$(30\times 9.8)\times (2 m) = (45 \times 9.8) \times r_2$

$60 = 45 r_2$

$r_2 = \frac{60}{45}$

$r_2 = 1.33 m$

so girl distance from fulcrum must be 1.33 m