**Answer: Option A**

Refer to the video tutorial for the explanation.

**Answer: Option A**

Refer to the video tutorial for the explanation.

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For Combined Science Physics Olevel, when constructing vector diagram, a method called **Parallelogram Method** is commonly used.

**Parallelogram Method** is used when **2 forces are known**, and the** resultant (net) force R**, can be found.

Below show **5 different variations of questions** when can be solved by using Parallelogram Method:

(A) Body has **acceleration**, **forces are unbalanced**, there is a **resultant force R** *(Newton’s 2nd law)*

(B) Body **at rest**, **all forces are balanced**, there is **no resultant force R** *(Newton’s 1st law)*

(C) Body moving at **constant velocity**, **all forces are balanced**, there is n**o resultant force** *(Newton’s 1st law)*

(D) Finding **unknown force** (with **resultant force R + another known force are given**)

(F) **Vector diagram is applicable to all vector quantities **(with magnitude and direction). Not just for forces.

Click here to view video tutorials on how to construct parallelogram step-by-step

For Pure Physics, another method is the closed-loop triangle, where only 1 known force with 2 other unknown force. Click here to view the video tutorials.

For Combined Science (Physics), drawing of vector diagram is a must.

In general, **two known forces** are given and **the resultant force of these two forces** is to be found using the **vector diagram**.

There are two methods to draw vector diagram 1) **Parallelogram method** and 2) **Tip-to-tail method. **In this post, the parallelogram method is used.

**Example 02**

**Example 03**

**Example 04**

Click here to view another post on Closed-Loop Triangle Method (2 forces, 2 unknowns, 1 known)

Click here to view how parallelogram method is applied to various kind of questions

**Vector diagram** is commonly referred to **parallelogram rule**.

Vector diagrams are generally divded into 3 categories:

**1)** 2 forces acting on a body, there is a resultant force. (Newton’s 2nd Law)

**2)** 3 forces acting on a body, the body is ** at rest / in equilibrium** or moving at

– The resultant force due to any 2 forces is

**3)** 3 forces acting on a body, the body is ** at rest / in equilibrium** or moving at

– Only 1 known force, angles given, using

Let’s look at some examples for each category.

**1) 2 forces acting on a body, there is a resultant force. (Newton’s 2nd Law)**

**2) 3 forces acting on a body, the body is at rest / in equilibrium or moving at constant speed. (Newton’s 1st Law, Net force = 0N)**

Example 1: Body at rest – Using Parallelogram Rule

Example 1: Body at rest – Using Closed-Looped Triangle

Example 2: Body at constant speed – Using Parallelogram Rule

Example 2: Body at constant speed – Using Closed-Looped Triangle

**3) 3 forces acting on a body, the body is at rest / in equilibrium or moving at constant speed (Newton’s 1st Law, Net force = 0N)**

Click here to view the construction of vector diagram using Parallelogram Method.

A trolley is acted on by three forces, P, Q and R in magnitude and direction as shown in the figure below. A single force F could balance all three forces. What is the magnitude of F?

Solutions:There are 3 different forces, P, Q and R acting on the trolley.Consider the forces P and R only, as they are acting perpendicular to each other, the resultant force falls exactly on Q. (using the vector diagram method/parallelogram method).The resultant of P and R is Q, plus the existing Q, will give a **final resultant force of 2Q** acting on the trolley.

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