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

##### June 20, 2019

**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} m^{2} Pressure P_{a} = F/A = 1.5 /(2 x 10^{-6}) = 7.5 x 10^{5} Pascal**

**Nail B**

Force F = 1.5 N

Area A= 6 mm^2 = 6 x 10

Pressure P

Force F = 1.5 N

Area A= 6 mm^2 = 6 x 10

^{-6}m^{2}Pressure P

_{a}= F/A = 1.5 /(6 x 10^{-6}) = 2.5 x 10^{5}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 cm**

^{2}= 96 x 10

^{-4 }m

^{2}

**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 cm ^{2} = 100 x 10^{-4} m^{2} = 10^{-2} m^{2} Thrust = Pressure x area = 14700 * 10^{-2} = 147 N**