Question

A s=3.35-m-long rigid beam with a mass of 97.3 kg is supported at each end. An 88 kg student stands d=1.8 m from support 1. How much upward force does left support exert on the beam?

Answer 1

i determined the torque of the student and each of the beams but i dont know what to do from there.

Answer 2

do you need the picture?

Answer 3

The forces from the two supports must cancel the force of gravity so that the beam and the student do not fall.

Answer 4

yes i understand that but how can i determine the upward forces of the left and the right supports?

Answer 5

hey are you still there?

Answer 6

You have two "unknowns," the forces from each support. You should have two different equations that relate them; the torque should be zero, and the forces must cancel the gravitational force acting on the beam and student. They are linear equations and the system can be solved for each support force.

Answer 7

ok can you please explain it because i tried solving it several ways and it keep saying that I am wrong

Answer 8

You have to pick an origin of rotation when calculating torque. I suggest using the location of one of the forces as an origin. The beam's gravitational force can be thought of as acting on the center of the beam when calculating torque.

Answer 9

i choice for the first supp be the origin (the left one) and from there i calculated the weight of the beam from the center of mass (97.3 kg)(9.8) to get a weight of 953.54 and since the force of the mass is going down i choice that to be my negative direction so -953.54 N.

Answer 10

then i calculated the forces acting on the student which is just his weight do (88)(9.8)= 862.4 going in the negative direction.

Answer 11

then i broke down all the forces in a free body diagram and i calculated the torque of the student, left support and right support and from there i am lost. Like I determined the torque fpr the student (88)(9.8)(1.8)= -1552.32 N*m, torque of the weight (3.35/2)(9.8)(97.3)= -1559.1795 and the torque of the support on the right side (3.35 F) but then im lost. can you please clarify what im doing wrong and what to do from here .

Answer 12

forget it i figured it out.