## Mechanical Properties of Fluids Questions and Answers Part-5

1. The property utilized in the manufacture of lead shots is
a) Specific weight of liquid lead
b) Specific gravity of liquid lead
c) Compressibility of liquid lead
d) Surface tension of liquid lead

Answer: d
Explanation: Surface tension of liquid lead

2.The dimensions of surface tension are
a) $\left[MLT^{-1}\right]$
b) $\left[ML^{2}T^{-2}\right]$
c) $\left[ML^{0}T^{-2}\right]$
d) $\left[ML^{-1}T^{-2}\right]$

Answer: c
Explanation:

3. A wooden stick 2m long is floating on the surface of water. The surface tension of water 0.07 N/m. By putting soap solution on one side of the sticks the surface tension is reduced to 0.06 N/m. The net force on the stick will be
a) 0.07 N
b) 0.06 N
c) 0.01 N
d) 0.02 N

Answer: d
Explanation:

4. The force required to take away a flat circular plate of radius 2 cm from the surface of water, will be (the surface tension of water is 70 dyne/cm)
a) $280\pi$  dyne
b) $250\pi$  dyne
c) $140\pi$  dyne
d) $210\pi$  dyne

Answer: a
Explanation: Force required, F = 2 $\pi$ rT = 2 $\pi$ * 2 * 70 = 280 $\pi$ Dyne

5.Surface tension may be defined as
a) The work done per unit area in increasing the surface area of a liquid under isothermal condition
b) The work done per unit area in increasing the surface area of a liquid under adiabatic condition
c) The work done per unit area in increasing the surface area of a liquid under both isothermal and adiabatic conditions
d) Free surface energy per unit volume

Answer: a
Explanation: The work done per unit area in increasing the surface area of a liquid under isothermal condition

6.Energy needed in breaking a drop of radius R into n drops of radii r is given by
a) $4\pi T\left(nr^{2}-R^{2}\right)$
b) $\frac{4}{3}\pi \left(r^{3}n-R^{2}\right)$
c) $4\pi T\left(R^{2}-nr^{2}\right)$
d) $4\pi T\left(nr^{2}+R^{2}\right)$

Answer: a
Explanation:

7.The potential energy of a molecule on the surface of liquid compared to one inside the liquid is
a) Zero
b) Smaller
c) The same
d) Greater

Answer: d
Explanation: Greater

8. Two droplets merge with each other and forms a large droplet. In this process
a) Energy is liberated
b) Energy is absorbed
c) Neither liberated nor absorbed
d) Some mass is converted into energy

Answer: a
Explanation:

9. A drop of liquid of diameter 2.8 mm breaks up into 125 identical drops. The change in energy is nearly (S.T. of liquid =75 dynes/cm)
a) Zero
b) 19 erg
c) 46 erg
d) 74 erg

Answer: d
Explanation:

10. Radius of a soap bubble is 'r', surface tension of soap solution is T. Then without increasing the temperature, how much energy will be needed to double its radius
a) $4\pi r^{2} T$
b) $2\pi r^{2} T$
c) $12\pi r^{2} T$
d) $24\pi r^{2} T$

Answer: d
Explanation: