24. Melting of wax is a physical change but burning of wax is a chemical change. Explain.
Answers
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
Answer:
(a) Photosynthesis → Chemical change
(b) Dissolving sugar in water → Physical change
(c) Burning of coal → Chemical change
(d) Melting of wax → Physical change
(e) Beating aluminium to make aluminium foil → Physical change
(f) Digestion of food → Chemical change
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