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September 18, 2019

Solution to problems – class 9 – Set 1 Q49, Q50, Q51


49) A hammer exerts a force of 1·5 N on each of the two nails A and B. The area of cross section of tip of nail A is 2 mm^2 while that of nail B is 6 mm^2. Calculate pressure on each nail in pascal.

Solution
Nail A

Force F = 1.5 N
Area A= 2 mm^2 = 2 x 10-6 m2
Pressure Pa = F/A = 1.5 /(2 x 10-6) = 7.5 x 105 Pascal

Nail B
Force F = 1.5 N
Area A= 6 mm^2 = 6 x 10-6 m2
Pressure Pa = F/A = 1.5 /(6 x 10-6) = 2.5 x 105 Pascal

50) A block of iron of mass 7·5 kg and of dimensions 12 cm x 8 cm x 10 cm is kept on a table top on its base of side 12 cm x 8 cm. Calculate: (a) thrust and (b) pressure exerted on the table top. Take 1 kgf=10 N.

Solution
mass of iron block = 7.5 kg

Weight = mg = 7.5 x 10 N = 75 N

Area on which the thrust acts = 12 cm * 8 cm = 96 cm2 = 96 x 10-4 m2

Pressure exerted on the table top = force/area = 75/(96 x 10-4) = 7812.5 Pascal

51) A vessel contains water up to a height of 1·5 m. Taking the density of water 10^3 kg /m^3, acceleration due to gravity 9·8 m/ S^2 and area of base of vessel 100 cm^2, calculate: (a) the pressure and (b) the thrust, at the base of vessel.

Solution
Pressure = h d g = 1.5 x 1000 x 9.8 Pascal = 14700 Pascal
Area = 100 cm2 = 100 x 10-4 m2 = 10-2 m2
Thrust = Pressure x area = 14700 * 10-2 = 147 N

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