A uniform lever arm is used in conjunction with a pivot to weigh an object A. th

ID: 2142904 • Letter: A

Question

A uniform lever arm is used in conjunction with a pivot to weigh an object A. the mass of the lever arm

is not negligible but is unknown. The pivot point may be moved relative to the lever arm.

a) Where should the pivot be placed along the lever arm so that the mass of the lever arm does

not appear in the calculation?

b) If the unknown mass is balanced by a 0.5 kg mass hung from the lever arm 1.5 m from the

pivot point, how much does the unknown mass weigh given that it is hung from the lever arm

at a point 3 m on the other side of the pivot point?

a) Clearly the pivot should be place in middle so that weight of lever arm is distributed equally on both sides.

b) for this we need to balance torque

torque dut to known mass = 0.5*1.5 = 0.75

torque due to unknown mass = m*3

so m*3= 0.75 = so m = 0.75/3 = 0.25

so weight of unknown mass = 0.25kg

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