A balloon lifting in air follows the following principle

In a two dimensional incompressible steady flow around an airfoil, the stream lines are 2 cm apart at a great distance from the airfoil, where the velocity is 30 m/sec. The velocity near the airfoil, where the stream lines are 1.5 cm apart, is

A. 22.5 m/sec.

B. 33 m/sec.

C. 40 m/sec.

D. 90 m/sec.

According to the principle of buoyancy a body totally or partially immersed in a fluid will be lifted up by a force equal to

A. the weight of the body

B. more than the weight of the body

C. less than the weight of the body

D. weight of the fluid displaced by the body

The difference of pressure between the inside and outside of a liquid drop is

A. $${\text{p}} = {\text{T}} \times {\text{r}}$$

B. $${\text{p}} = \frac{{\text{T}}}{{\text{r}}}$$

C. $${\text{p}} = \frac{{\text{T}}}{{2{\text{r}}}}$$

D. $${\text{p}} = \frac{{2{\text{T}}}}{{\text{r}}}$$

Fluid is a substance that

A. cannot be subjected to shear forces

B. always expands until it fills any container

C. has the same shear stress.at a point regardless of its motion

D. cannot remain at rest under action of any shear force