Question

c) Three weights are placed on a weightless plank AB. The Girst of mass 15 kg is placed 0.6 m from A, the second of mass 12 kg is placed 1.5 m from A and the third of mass 18 kg is placed 3 m from A. Determine the resultant moment upon the plank AB about A in SI units

Answer 1

Given that,

First mass = 15 kg

Distance from A = 0.6 m

Second mass = 12 kg

Distance from A = 1.5 m

Third mass = 18 kg

Distance from A =3 m

For first mass,

We need to calculate the moment about A

Using formula of moment

$M_{1}=m_{1}\times d_{1}$

Where, m = mass

d = distance

Put the value into the formula

$M_{1}=15\times0.6$

$M_{1}=9\ kg-m$

For second mass,

We need to calculate the moment about A

Using formula of moment

$M_{2}=m_{2}\times d_{2}$

Where, m = mass

d = distance

Put the value into the formula

$M_{2}=12\times1.5$

$M_{2}=18\ kg-m$

For third mass,

We need to calculate the moment about A

Using formula of moment

$M_{3}=m_{3}\times d_{3}$

Where, m = mass

d = distance

Put the value into the formula

$M_{3}=18\times3$

$M_{3}=36\ kg-m$

We need to calculate the resultant moment upon the plank AB about A

Using formula of moment

$M=M_{1}+M_{2}+M_{3}$

Put the value into the formula

$M=9+18+36$

$M=63\ kg-m$

Hence, The resultant moment upon the plank AB about A is 63 kg-m.