Use the worked example above to help you solve this problem. A woman of mass m 5

Question

Use the worked example above to help you solve this problem. A woman of mass m 50.5 kg sits o the le ft end o f a seesaw a plank of ength L 4.28 m-pivoted n the m ddle as shown in the figure (a) First compute the torques on the seesaw about an axis that passes through the pivot point. Where should a man of mass M 68.3 kg sit if the system (seesaw plus man and woman) is to be balanced? 1.58 (b) Find the normal force exerted by the pivot if the plank has a mass of mpl 10.2 kg. 1.26e3 (c) Repeat part (a), but this time compute the torques about an axis through the left end of the plank. 1.57 EXERCISE HINTS GETTING STARTED I l'M STUCK! Suppose a 32.1 kg child sits 1.46 m to the left of center on the same seesaw as the problem you just solved. A second child sits at the end on the opposite side, and the system is balanced (a) Find the mass of the second child. m child 2 23.43 Use the pivot as the reference point because then two of the four forces on the plank exert zero torque. Which two? Since the plank is at rest, the torques due to the other two forces must balance kg (b) Find the normal force acting at the pivot point. Fn 544.2 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

Explanation / Answer

you have to use the equation x=mL/2M which was found in the example. You also have to use some of the measurements from the previous example in this problem.

a) 2.14m was half of the length of the seesaw so this is x. m, L are also given so you just plug the numbers x=2.14, m=32.1 kg, and L=1.46 m. You get M to be 10.95 kg, but since the entire seesaw was 4m long you have to double it. Therefore, the mass of the second child is 21.9kg.

b) using the mass of the first child, second child, and weight of the seesaw board (10.2 kg which came from book example) you use the equation

n=(m1 + m2 + m3)(g) g=gravity=9.80 m/s^2
n= (32.1 kg + 21.9 kg + 10.2 kg) (9.80 m/s^2)
n=629.16 N

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