a boy of mass 40kg sits at point 2m from the pivot of a see-saw . find the weight if a girl who can balance the see-saw by sitting at a distance of 3•2m from the pivot.( take g=10NKg)

The weight of the girl is 250 N

Explanation:

Static Equilibrium

Static equilibrium occurs when an object is at rest, i.e., neither rotating nor translating.

In the static rotational equilibrium, the total torque is zero with respect to any rotational axis.

The torque applied by a force F perpendicular to a displacement X with respect to a reference rotating point is:

T = F*X

The seesaw will be in rotational equilibrium if the torque applied by the boy of mass m1=40 Kg at x1=2 m from the pivot is equal to the torque applied by the girl of unknown mass m2 at x2=3.2 m from the pivot.

The force applied by both children is their weight:

It must be satisfied:

Simplifying:

Solving for m2:

Her weight is:

The weight of the girl is 250 N

work: w = fd (given)

work done by chet   =50*1 = 50 j

work done by mika =40*2 = 80 j

work done by sara =30*1.5 = 45 j

work done by bill =60*0.5 = 30 j

students in order from the greatest amount of work done to the least is mika> chet> sara> bill

hence option (b) is correct.