Question

If burning a candle wax is chemical reactions.why?

Answer 1

It is both physical and chemical change.The physical change occurs when the heat displaces the bonds that solidify the wax. Upon cooling, the wax is able to form the bond again. The chemical changes are much more complex. The first change is that the heat (fire) consumes the oxygen and fuels the flame. This then leads to the production and emission of carbon dioxide from the flame. As a by-product of the wick burning, you will then achieve soot as another physical and chemical change. The soot is a by product of the wick (chemical) and leaves a solid product as the emit (physical).

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Answer 2

Question

The diameter of a semicircular table is 10 cm. Find the cost of polishing the semicircular table at the rate of ₹3.50 per sq.cm.

Answer

Diameter of a semicircular table = 10cm

Radius of the semicircular table

\begin{gathered} = (\frac{diameter}{2} ) \\ = ( \frac{10}{2} )cm \\ = 5cm\end{gathered}

=(

2

diameter

)

=(

2

10

)cm

=5cm

Area of the semicircular table

\begin{gathered} = (\frac{\pi {r}^{2} }{2}) \\ = ( \frac{22}{7} \times 5 \times 5 \times \frac{1}{2} ) {cm}^{2} \\ = 39.285 {cm}^{2} \end{gathered}

=(

2

πr

2

)

=(

7

22

×5×5×

2

1

)cm

2

=39.285cm

2

Cost of polishing the semicircular table at the rate of ₹3.50cm²

\begin{gathered} = ₹(39.285 \times 3.50) \\ = ₹137.4975\end{gathered}

=₹(39.285×3.50)

=₹137.4975

More Information

Surface Area of Cuboid = 2(lb+bh+lh)

Surface Area of Cube = 6(side)²

Area of four walls = 2(l+b)h

Lateral Surface Area of Cuboid = 2(l+b)h

Lateral Surface Area of Cube = 4(side)²