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Problem Two people (a child and a parent) are sitting on a teeter-totter of length L = 3 m and mass m = 10 kg. There is a single support in the middle. The adult has a mass of m1 = 75 kg and the child has a mass of m2 = 30 kg. Draw a free body diagram for the system consisting of the people and teeter-totter. (6) If the child sits on the left end of the teeter-totter, where must the adult sit (relative to the support) to balance it? Problem 8: A 60 kg person is about to walk on a uniform plank. The 45 kg plank rests on two pivots as shown: (a) The person is between the pivots, distance D from the left end. Determine the normal force exerted by each pivot. Use D = 1.5 m, S = 3.75 m, and L = 6 m. The person is now on the far right. How far can he walk past the second pivot (H) before the whole thing tips?
Added by David S.
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The forces acting on the system would be the weight of the adult and child acting downwards, and the reaction force from the support acting upwards. To balance the teeter-totter when the child is on the left end, the adult must sit at a distance of (m2/m1) times Show more…
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A plank of wood of length 4.00 m with a fulcrum (pivot) at its center forms a seesaw. Suppose a child of mass 30.0 kg sits 1.50 m to the left of center, and a second child sits at the end on the far right side. The system is in equilibrium. Find the mass of the second child. (options: 30.0 kg, 22.5 kg, 7.5 kg, 40.0 kg) For the same setup with the two children sitting on the seesaw used in question 4, except now the first child's mass is 33.333 kg and the second child's mass is known to be 25 kg, find the normal force acting at the pivot point (fulcrum). The mass of the seesaw is 12.5 kg. (Hint: Remember if you can show the system is in equilibrium, then you can set the sums of forces/torques to zero and solve for whichever quantity you want.) Options: 804 N, 515 N, 695 N, 486 N
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2) Two children, one with a mass of 120kg and the other with a mass of 3kg, sit on a see-saw. The pivot point (axis of rotation) is directly below the center of mass of the see-saw plank, which has a mass of 20kg. a) The see-saw is in rotational equilibrium, and child one sits 1.5m from the pivot point. Determine how far from the pivot point child two sits. b) The plank is moved so that the center of mass of the plank is 0.75m to the left of the pivot point, as shown. Child one is still sitting 1.5m from the pivot point. Determine how far from the pivot point child two sits now. The mass of the plank is 20kg.
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Suppose two children are sitting on a seesaw as shown in the diagram at right. The seesaw has a length of 4.0 m, a mass of 40 kg, and is free to pivot around the fulcrum located right in the middle. Child 1 has a mass of 50 kg and is located 1.2 m from the fulcrum. Child 2 has a mass of 30 kg and is located a distance Tz away from the fulcrum. Draw a point free body diagram for the plank of the seesaw (not including the fulcrum). (Hint: there should be 4 forces acting on it, only one of them should be the weight force.) Determine the magnitude of all the downward forces.
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