Question

Q.No : 7. What will be total cost of polishing curved surface of a wooden cylinder at rate of rs. 20 per sq.M, if it has 40 cm diameter and 7m height?Rs. 480rs. 384rs. 352rs. 176

Answer 1

To calculate the cost of polishing of circular table, we have to calculate its area first of all.Here, Given diameter of the circular table-top = 1.6 m. Hence, r = 0.8 m

Area = π r2
= 3.14 × 0.8 × 0.8 = 2.0096 sq m

Cost of polishing = Rate × Area
= Rs 15 × 2.0096 = Rs 30.144

4.6

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Answer 2

Answer:

₹$176$

Explanation:

Given∶

Diameter of the wooden cylinder $= d = 40 cm = 40/100 m = 0.4 m$

Height of the wooden cylinder $= h = 7 m$

Cost of polishing $=$₹$20$ per $m^{2}$

Calculation∶

Radius of the wooden cylinder $= r = d/2 = 0.2 m$

Curved surface area of the wooden cylinder $= 2$π$rh$ $= 2 * 22/7 * 0.2 * 7 =$ $8.8 m^{2}$

Total cost of polishing $= 8.8 * 20 =$ ₹$176$

• Polishing helps in reducing the friction.
• On excessively polishing the surface, the bonds of the atoms on the surface start breaking which leads to increase in the irregularities on that surface.
• Friction is the opposing force experienced when two bodies slide over one another.
• Now the reason for increase in the friction on excessive polishing is that on polishing the surface beyond a certain limit, the atoms on the surface of the material start getting removed and the surface molecules exert strong attractive forces on each other which creates new irregularities on that surface and the friction starts increasing.

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