Introduction to Linear Polynomials | EOT

Question 9

The work done by a body on the application of a constant force is the product of the constant force and the distance travelled by the body in the direction of the force. Express this in the form of a linear equation in two variables (work $w$ and distance $d$ ), and draw its graph by taking the constant force as 3 units. What is the work done when the distance travelled is 2 units? Verify it by plotting it on the graph.

Solution

Understand the Question

The work done ( $w$ ) is the product of constant force and distance travelled ( $d$ ): $\text{Work done} = \text{Constant force} \times \text{Distance}$
Given a constant force of $3\text{ units}$ , the relation becomes a linear equation in two variables: $w = 3d$ .
We plot this straight line by finding coordinates $(d, w)$ and use both the equation and the graph to determine the work done when $d = 2\text{ units}$ .

Step 1 · Form the Linear Equation

Given $\text{Work done} = \text{Force} \times \text{Distance}$

Let work done be $w$ and distance travelled be $d$ . Taking constant force $= 3\text{ units}$ : $w = 3d$

Step 2 · Find Points and Plot the Graph

Find values of $w$ for different values of $d$ :

When $d = 0$ , $w = 3(0) = 0 \implies (0, 0)$
When $d = 1$ , $w = 3(1) = 3 \implies (1, 3)$
When $d = 2$ , $w = 3(2) = 6 \implies (2, 6)$

\begin{array}{|c|c|c|c|} \hline d & 0 & 1 & 2 \\ \hline w = 3d & 0 & 3 & 6 \\ \hline (d, w) & (0, 0) & (1, 3) & (2, 6) \\ \hline \end{array}

Step 3 · Calculate and Verify Work Done for $d = 2$

From the linear equation $w = 3d$ , substitute $d = 2\text{ units}$ :

\begin{aligned} w &= 3 \times 2 \\ &= 6\text{ units} \end{aligned}

From the graph, locating $d = 2$ on the horizontal axis and moving vertically to the line gives the point $(2, 6)$ , which corresponds to $w = 6\text{ units}$ on the vertical axis.

Answer

The linear equation is $w = 3d$ .

When the distance travelled is $2\text{ units}$ , the work done is $6\text{ units}$ .

Common Mistakes

Swapping Variables: Writing $d = 3w$ instead of $w = 3d$ . Work done is dependent on distance, so $w$ is the product of force and $d$ .
Missing Units: Forgetting to write "units" with the calculated work done ( $6\text{ units}$ ).
Axis Misalignment: Confusing the axes when plotting—distance $d$ is taken on the horizontal axis and work $w$ on the vertical axis.

More questions in EOT

Write a polynomial of degree 3 in the variable $x$ , in which the coefficient of the $x^2$ term is $-7$ .

Find the values of the following polynomials at the indicated values of the variables.

(i) $5x^2 - 3x + 7$ if $x = 1$

(ii) $4t^3 - t^2 + 6$ if $t = a$

If we multiply a number by $\dfrac{5}{2}$ and add $\dfrac{2}{3}$ to the product, we get $\dfrac{-7}{12}$ . Find the number.

A positive number is 5 times another number. If 21 is added to both the numbers, then one of the new numbers becomes twice the other new number. What are the numbers?

If you have ₹800 and you save ₹250 every month, find the amount you have after:

(i) 6 months

(ii) 2 years

Express this as a linear pattern.

The digits of a two-digit number differ by 3. If the digits are interchanged, and the resulting number is added to the original number, we get 143. Find both the numbers.

Draw the graph of the following equations, and identify their slopes and $y$ -intercepts. Also, find the coordinates of the points where these lines cut the $y$ -axis.

(i) $y = -3x + 4$

(ii) $2y = 4x + 7$

(iii) $5y = 6x - 10$

(iv) $3y = 6x - 11$

Are any of the lines parallel?

If the temperature of a liquid can be measured in Kelvin units as $x \text{ K}$ and in Fahrenheit units as $y^{\circ}\text{F}$ , the relation between the two systems of measurement of temperature is given by the linear equation $y = \dfrac{9}{5}(x - 273) + 32$ .

(i) Find the temperature of the liquid in Fahrenheit if the temperature of the liquid is $313 \text{ K}$ .

(ii) If the temperature is $158^{\circ}\text{F}$ , then find the temperature in Kelvin.

Q10

*10. The graph of a linear polynomial $p(x)$ passes through the points $(1, 5)$ and $(3, 11)$ .

(i) Find the polynomial $p(x)$ .

(ii) Find the coordinates where the graph of $p(x)$ cuts the axes.

(iii) Draw the graph of $p(x)$ and verify your answers.

Q11

*11. Let $p(x) = ax + b$ and $q(x) = cx + d$ be two linear polynomials such that:

(i) $p(0) = 5$ .

(ii) The polynomial $p(x) - q(x)$ cuts the $x$ -axis at $(3, 0)$ .

(iii) The sum $p(x) + q(x)$ is equal to $6x + 4$ for all real $x$ .

Find the polynomials $p(x)$ and $q(x)$ .

Q12

*12. Look at the first three stages of a growing pattern of hexagons made using matchsticks. A new hexagon gets added at every stage which shares a side with the last hexagon of the previous stage.

(i) Draw the next two stages of the pattern. How many matchsticks will be required at these stages?

(ii) Complete the following table.

(iii) Find a rule to determine the number of matchsticks required for the $n^{\text{th}}$ stage.

(iv) How many matchsticks will be required for the $15^{\text{th}}$ stage of the pattern?

(v) Can 200 matchsticks form a stage in this pattern? Justify your answer.

Q13

*13. Let $p(x) = ax + b$ and $q(x) = cx + d$ be two linear polynomials such that:

(i) The graph of $p(x)$ passes through the points $(2, 3)$ and $(6, 11)$ .

(ii) The graph of $q(x)$ passes through the point $(4, -1)$ .

(iii) The graph of $q(x)$ is parallel to the graph of $p(x)$ .

Find the polynomials $p(x)$ and $q(x)$ . Also, find the coordinates of the point where these lines meet the $x$ -axis.

Q14

*14. What do all linear functions of the form $f(x) = ax + a, a > 0$ , have in common?