Question

Three weights are placed on a massless seesaw. A $1kg$ weight is placed at $x=3m$ and a $2kg$ weight at $x=-1m$. The fulcrum of the seesaw is at $x=0m$.
Which of the following mass / location combinations would balance the seesaw?

• A. No additional weights are necessary
• B. $m=0.25kg,x=-4m$
• C. $m=3kg,x=0.5m$
• D. $m=2kg,x=0.5m$
• E. $m=1kg,x=-1m$

Answer 1

Answer: (B), (E)

The correct options are
B $m=0.25kg,x=-4m$
E $m=1kg,x=-1m$

The net torque acting on the seesaw about the fulcrum=$\left[\right(1\left)\right(3)-(2\left)\right(1\left)\right]N-m$

$=1N-m$

Hence the torque due to the third mass must be $-1N-m$

Considering option E, the torque due to that mass=$-\left(1\right)\left(1\right)N-m=-1N-m$

Hence answer is option A and E.