In this worksheet, we will practice solving problems involving the resultant of a set of coplanar forces acting at a point geometrically using a polygon of forces.
Dina is attempting a mechanics problem in which four coplanar forces , , , and are acting on a body. She needs to determine whether the body is in equilibrium or not. She remembers her teacher saying something about checking whether she could arrange the forces into a polygon. So, she has drawn the shown parallelogram.
Dina concludes that the forces are in equilibrium. Is she correct?
Which of the following best describes what she has done?
- AShe has got the right answer. However, her figure is wrong. She has not paid attention to the direction of the forces. All the forces should meet head-to-tail, whereas, in her diagram, and meet head-to-head and and meet head-to-head. However, since the forces form a parallelogram, she can swap and over and she will have a correct diagram.
- BShe has got the wrong answer because she has not arranged the forces in numerical order.
- CShe has got the wrong answer because all the forces should meet head-to-tail, whereas, in her diagram, and meet head-to-head and and meet head-to-head. So, the forces do not form a polygon and they are not in equilibrium.
- DShe has got the right answer using the right method.
- EShe has got the right answer. However, her figure is wrong; she has not paid attention to the order of the forces. She should have arranged the forces in numerical order.
Six coplanar forces , , , , , and are acting on a body in equilibrium. Their polygon of forces is shown.
Given that , , , , and , find the magnitude of .
- A newtons
- B 19 newtons
- C newtons
- D newtons
- E 6 newtons