Physics Balancing Forces

[k.rotelli]

O Question 17 (Cod. : Simu4515_e)
Subject: LOGIC
A metal bar 1 metre long is suspended by its centre. At 10 cm from the right end hangs a 10 kg weight, while at the other end hangs a 36 kg weight. What must you do to balance the bar and keep it in the horizontal?
A: Add to the weight hung on the right end another weight of 35 kg
B: Nothing, the bar is already balanced
C: Add to the weight hung on the left end another weight of 28 kg
D: Add to the weight hung on the left end another weight of 35 kg E: Add to the weight hung on the right end another weight of 28 kg

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[Juliette]

Hi!

• the pivot is at the center of the beam so we can ignore the moment of the beam
• the 36 kg weight is at the very end of the left side of the beam, so 50cm from the pivot
• sum of clockwise moments = sun of counter clockwise moments

counter clockwise: moment = 36 * 10 * 50 = 18000
clockwise: moment = Fd = mgd = 10 * 10 * 40 = 4000

40 * 10 * (10 + X kg) = 18000 for the beam to balance
35 = X

we must add 35 kg to the weight hung on the right to balance

Hope this helps!

[k.rotelli]

Thanks Juliette - super clear and easy to understand now