What is the net torque acting on a teeter totter 10 feet lon

What is the net torque acting on a teeter totter 10 feet long (fulcrum is at the center) if a 59 pound child is on the left side 4.5 feet from the center and a 98 pound child is on the right side 3.1 feet from the center.

Multiple choice

a) -569.3 ft-lbs

b) -38.3 ft-lbs

c) 569.3 ft-lbs

d) 38.3 ft-lbs

Solution

solution:

torque can be calculated as Force*lever arm

59 pound child is on the left side 4.5 feet from the center

so torque produce by him at centre= 59*4.5=265.5 ft lbs anticlockwise

now

98 pound child is on the right side 3.1 feet from the center.

so torque produce by him at centre= 98*3.1=303.8ft lbs clockwise

net torque = (303.8-265.5)ft lbs clockwise

= 38.3 ft lbs clockwise

as clockwise torque is negative

hence

-38.3 ft lbs

b option