Moments and centres of mass of discrete masses Quiz

1. A force of 20 N acts at a perpendicular distance of 0.3 m from a pivot. What is its moment about the pivot?

• A. $60$ N m
• B. $6$ N m
• C. $0.015$ N m
• D. $20.3$ N m

2. A 1 kg particle is at $x=0$ and a 3 kg particle at $x=8$. Where is the centre of mass?

• A. $x=4$
• B. $x=2$
• C. $x=8$
• D. $x=6$

3. A uniform rod $AB$ of length 5 m and mass 8 kg is supported at $A$ and at $C$, where $AC=4$ m. What is the reaction at $C$ ($g=9.8$)?

• A. $49$ N
• B. $39.2$ N
• C. $62.7$ N
• D. $98$ N

4. Particles of 2 kg at $(0,0)$, 3 kg at $(5,0)$ and 5 kg at $(0,4)$. What is the $x$-coordinate of the centre of mass?

• A. $2.5$
• B. $1.67$
• C. $1.5$
• D. $3$

5. A 6 kg system has its centre of mass at $x=2$. A 2 kg particle is added at $x=10$. Where is the new centre of mass?

• A. $x=6$
• B. $x=4$
• C. $x=3$
• D. $x=8$