Physics MCQs for Class 11 on “Fluids Mechanical Properties Pressure – 2”.
1. A nail is made pointed at its end to ensure that pressure is more for a given amount of force applied on it. True or False?
a) True
b) False
Answer: a
Clarification: Pressure is defined as force per unit area. And we need more pressure to drive the nail easily into the wall. So we make the nail pointed as it has a much lesser area than a blunt end.
2. Which device is used to measure pressure?
a) Odometer
b) Barometer
c) Dynamometer
d) Hydrometer
Answer: b
Clarification: Barometer is a device used to measure air pressure. Odometer is a device used to measure the distance travelled by a wheeled vehicle (it is the speed indicator in your vehicle). Dynamometer is a device used to measure torque or rpm of an engine. Hydrometer is used to measure specific gravity of liquids. Also keep in mind that the liquid used in a barometer is mercury.
3. Which of the following quantities has the same S.I. unit as that of pressure?
a) Work
b) Energy / Velocity
c) Energy / Displacement
d) mass X (velocity)2/Volume
Answer: d
Clarification: The S.I. unit of pressure is N/m2.
Work has the unit of Nm.
Energy/Velocity has the unit of Nm/(m/s) = Ns.
The unit of energy/disp is Nm/m = N.
The unit of mass X (velocity) 2/Volume is same as that of energy per unit volume because mass X (velocity)2 is equal to energy,
which is in turn equal to Nm/m3 = N/m2, therefore this is the correct option.
4. Pressure is a vector quantity. True or False?
a) True
b) False
Answer: b
Clarification: When we talk about pressure at a point, we say it is exerted in all directions at that point, so it is not a vector quantity. As a vector quantity should have fixed direction with magnitude.
5. Assume a force of 30 N is distributed over a surface of area 2m2 in such a way that at each point force can be considered to act at an angle of 30° to the normal at that point. What will be the value of pressure on that plane?
a) 7.5 Pa
b) 7.5(sqrt{3}) Pa
c) 15 Pa
d) 15(sqrt{3}) Pa
Answer: b
Clarification: One important thing to keep in mind is that pressure at a point is the normal component of force per unit area, NOT total force per unit area.
So, here we will take the normal component of 30N force, i.e:
30cos(30°)=15(sqrt{3}).
Press = F/A = 15(sqrt{3})/2
= 7.5(sqrt{3}) Pa.
6. A car containing a beaker of water is moving horizontally on a level road. Consider two points, A & B, inside the water such that they are on the same horizontal level and are separated by a distance L. Which of the following options is correct regarding the pressure differences between those two points?
a) If car is accelerating with acceleration a, PA – PB = ρgL
b) If car is accelerating with acceleration a, PA – PB = 0
c) If car is moving with constant velocity, PA – PB = 0
d) If car is moving with constant acceleration a, PA – PB = ρ (g+a)L
Answer: c
Clarification: When the car is moving with constant velocity, points on the same horizontal level will have the same pressure.
So, PA – PB = 0.
When the car moves with constant acceleration the pressure difference between those two points will be ρaL,
as the pressure difference will be responsible for providing acceleration to the small fluid column of volume L*dA between points A & B
(where dA is an area of small element that we think of).