Notes of Chapter 06: Fluid Dynamics of “Physics XI” for FSc Part 1 published by kpk textbook Board, pesahwar. These notes are very helpful to prepare Physics paper of FSc Part 1 for Federal Board, mardan Board, swabi Board, swat Board, abbotabad Board, DG Khan Board, Rawalpindi Board or any other board of Punjab, Pakistan.
Conceptual Questions physics cha 6 fluid dynamics class 11
Q.1) From the top of a tall building, you drop two table-tennis balls, one filled with air and the other with water. Which ball reaches terminal velocity first and why?
The terminal velocity of an object is given by;
This shows that terminal velocity depends on density, size and shape of the object as well as the medium through which it travels. The two tennis balls are of same size and shape but their densities are different. From above relation we can see that
vT ∝ ρ
Hence the terminal velocity of air filled tennis ball will be reached first because its density is lighter than the tennis ball filled water. In other words the upward drag force becomes equal to mg sooner for lighter tennis ball.
Q.2) Why can a squirrel jump from a tree branch to the ground and run away undamaged, while a human could break a bone in such a fall?
Both squirrel and human fall under the action of gravity i.e. the force acting on them is given by;
F = mg
Since g is constant and mass of human is greater than that of mass of squirrel so a human would experience a large force as compared to that of squirrel. Hence he could break a bone unlike squirrel.
Q.3) How does the terminal speed of a parachutist before opening a parachute compare to the terminal speed afterward? Why is there a difference?
Before opening of parachute the weight is bigger force than air resistance so the skydiver accelerates downward unless it reaches the point where air resistance increases and become equal to weight i.e. the terminal velocity is achieved.
When parachute is opened the terminal velocity is reduced because now air resistance increases dramatically: it is much greater than the weight force, so the skydiver slows down. The air resistance force reduces until it becomes equal to weight and second terminal velocity is achieved.
Thus the difference in air resistance results in difference in terminal velocities before and after opening of parachute.
Q.4) You can squirt water over a greater distance by placing your thumb over the end of a garden hose, than by leaving it completely uncovered. Explain how this works?
From equation of continuity the crossectional area and the velocity of fluid are inversely related to each other to keep their product constant. Hence when we place our thumb over the end of a garden hose, its crossectional area is decreased and so, the velocity of water is increased due to which it can squirt over greater distance as compared to when it is left completely uncovered.
Q.5) Why does smoke rise faster in a chimney on a windy day?
As the wind blows across the top of the chimney, so the pressure over there will be less than that of inside. And Bernoulli’s principle for fluids tells us that it is nature of fluid that it always flows from area of high pressure to the area of lower pressure.
When a breeze is blowing, it will create a pressure difference between inside and outside of the chimney, which in turn causes faster rise of smoke in chimney.
Q.6) Two boats moving in parallel paths close to one another risk colliding. Why?
When the two boats moving in parallel path come close to one another the velocity of streamlines becomes very large between them as compared to velocity on the other sides. Owing to this the pressure between them becomes very low while the pressure on the other sides of the boat becomes very high. Due to this pressure difference the boats feel a push from the region of high pressure to the region of low pressure. Thus resulting in colliding.
Q.7) A cricket ball moves past an observer from left to right spinning counterclockwise. In which direction will the ball tend to deflect?
As the ball is spinning as well as moving in the forward direction so the spinning will make the motion of the ball faster, due to which pressure in that region decreases. Thus the pressure to the other side of the ball will be maximum.
When the ball will hit to the ground, then due to lower pressure to its side of rotation, it will get an extra curvature to that side and will swing to its direction of spinning.
Q.8) If aero-foil lift the aero-plane in upright position, how do the pilots make the aero-planes fly upside down?
The wings of aero-plane are designed in such a way that aero-foil is curved on the upper side due to which pressure above the wing is lower than underneath. This pressure difference allows the air to lift the wings upwards. In order to fly upside down, the wings of aero-plane are designed in such a way that these are curved from, both, upper and lower sides i.e. symmetric. Because of this pilot can fly the plane upside down just by altering the angle.
Q.9) Why do the golf balls have dimples?
Dimple on the golf balls are to minimize the swing of the ball. Because of the dimples frictional force is created between the ball and the air which minimizes the swing of ball and help it to go higher and farther.
Q.10) How by using wind deflectors on the top truck cabs reduce fuel consumption?
Wind deflectors are designed in such a manner that they reduce the air resistance offered by a vehicle or trailer truck. Thus lesser the air resistance experienced by the vehicle, the lesser the amount of work it has to be done to move forward.
Owing to this reason many trailer trucks use wind deflectors on the top of their cabs because in such a way the amount of work done against the air resistance is reduced significantly. Therefore, engine has to do less work done which will, in turn, lower the consumption of fuel in these trucks, especially when they have to travel in windy areas.
Physics Chapter 6 Fluid Dynamics: How To Solve The Problem
Notes of Chapter 06: Fluid Dynamics of “Physics XI” for FSc Part 1 published by kpk textbook Board, Peshawar. These notes are very helpful to prepare Physics paper of FSc Part 1 for Federal Board, mardan Board, swabi Board, swat Board, abbotabad Board, DG Khan Board, Rawalpindi Board or any other board of Punjab, Pakistan.
Notes of Chapter 06Fluid Dynamics
Hydrostatics: Introduction to Hydrostatics and Heat and Mass Transfer. Mathematics of the Navier-Stokes Theorem Heat and Mass Transfer: Theorems from Jacobi Equation and Navier-Stokes Equation are explained. Radial Displacement and Non-Radial Displacement Equations Study of Navier-Stokes and Non-Navier-Stokes Equations: The expression of the Navier-Stokes Equation the non-radial and radial displacements of a fluid the no-thickness condition and no-thinness condition Stokes Deformations of a Plane Water pressure and Heat: A practical approach on calculating the pressure and heat in the fluid. Practical pressure and heat equations in De-oxygenated Water the bulk density of water and temperature of water.
In the final analysis, the responsibility lies on the students, they should try to provide correct information to students about FSc subject but in all, this task is extremely hard, the assignment writing task is on an exceptionally great level, and you have to provide an answer of the question in an understandable way. All the best for your success.