Question

dont know what im doing wrong

Suppose a 28.4-kg child sits 0.67 m to the left of center on the same seesaw as the problem you just solved in the PRACTICE IT section. A second child sits at the end on the opposite side, and the system is balanced. (a) Find the mass of the second child. 8.55 kg (b) Find the normal force acting at the pivot point. 362 Your answers to part (a) and (b) are not consistent. Does the plank have weight? How will the weight of the plank affect the normal force? N Need Help?

Answer 1

(b)

It seems the answer didn't include the weight of the plank

Normal force at pivot = Weight of first child + Weight of second child + Weight of the plank

$F_{N}=m_{1}g+m_{2}g+m_{pl}*g$

$F_{N}=28.4kg*9.81m/s^{2}+8.55kg*9.81m/s^{2}g+13.6kg*9.81m/s^{2}$

$F_{N}=28.4*9.81+8.55*9.81+13.6*9.81$

$F_{N}=(28.4+8.55+13.6)*9.81$

$F_{N}=50.55*9.81$

ANSWER: ${\color{Red} F_{N}=495.9N}$

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