Tag: option b: engineering physics

Questions Related to option b: engineering physics

Choose the wrong statement.

  1. Viscous force always supports the motion.

  2. A denser fluid always more viscous than a less dense fluid.

  3. Any object cannot have a velocity after a sufficient long time more than its terminal velocity in a given fluid.

  4. If a body is at rest in a fluid then the viscous force on it is zero.


Correct Option: A
Explanation:

Viscous force is a frictional force which opposes the relative motion between liquid molecules. Terminal velocity is the velocity attained by the particle when net force on it becomes zero the body cannot have more velocity than terminal velocity in respective fluid.

The velocity of falling rain drops attains limited value because of :

  1. surface tension

  2. upthrust due to air

  3. viscous force exerted by air

  4. air current


Correct Option: C
Explanation:

Gravity does cause things to fall with increasing speed, but as they speed up viscous force by air increases increases. Since according to stokes law $F _r \propto v$.  Eventually the acceleration stops and the raindrop reaches a constant terminal velocity.

Clouds appear to float in air due to:

  1. low density.

  2. air current.

  3. viscosity of air.

  4. buoyancy.


Correct Option: C
Explanation:

Viscosity of air is responsible for floating of clouds is air

The quality of fountain-pen ink depends largely on:

  1. Surface tension of the liquid

  2. Viscosity of ink

  3. impurities in ink

  4. Density of ink


Correct Option: B
Explanation:

The quality of fountain-pen ink depends largely on viscosity of ink because as the viscosity of ink is more, it requires hard pressure on the pen to write and as the viscosity of ink is less  we can write smoothly.

Two identical lead shots are dropped at the same time in two glass jars containing water and glycerine. The lead shot dropped in glycerine descends slowly because:

  1. Viscous force is more in water than in glycerine

  2. Viscous force is more in glycerine than in water

  3. Surface tension is more in water

  4. Surface tension is more in glycerine


Correct Option: B
Explanation:

Glycerine viscosity is 950 cP and water viscosity is 0.89 cP. We can see that glycerine has high viscosity. High viscous force of glycerine increases the time of drop of lead shot than in water.

After the storm, the sea water waves subside due to:

  1. Surface tension of sea-water

  2. Disapperance of heavy currents

  3. The viscosity of sea water

  4. Gravitational pull of the storm


Correct Option: C
Explanation:

After the storm, the sea water waves subside due to the viscosity of sea water. Since viscosity's main cause is cohesive force which acts in intermolecular particles. So, sea water waves subside due to these cohesive force between water molecules.

A good lubricant must have:

  1. high viscosity

  2. low viscosity

  3. high density

  4. low surface tension


Correct Option: A
Explanation:

Good lubricant must have high viscosity. So, that machine parts can do work better. Higher the viscosity of the lubricants the greater is its ability to provide boundary lubrication, which means a boundary between moving parts. 

When stirring of a liquid is stopped, the liquid comes to rest due to:

  1. surface tension

  2. gravity

  3. viscosity

  4. buoyancy


Correct Option: C
Explanation:

When stirring of a liquid is stopped, the liquid comes to rest due to viscosity of liquid. While stirring fluid at the axis moves faster in circular path whereas the fluid in contact with the walls does not move. So, the viscous drag force acting between the fluid layers tries to restrict the relative motion of them. So, by viscous drag force liquid comes to rest. 

Coefficient of viscosity of a gas:

  1. increases with increase of temperature.

  2. decreases with increase of temperature.

  3. remains constant with increase of temperature.

  4. may increase or decrease with increase of temperature.


Correct Option: A
Explanation:

With increase in temperature, the molecule of gas carry more momentum and collide more often, that means more viscosity. So, coefficient of viscosity of a gas increases  with increase of temperature.

Viscosity of water at constant temperature is:

  1. more in deep water

  2. more in shallow waters

  3. less in deep water

  4. same in both deep water and shallow waters


Correct Option: A
Explanation:

In deep water temperature decreases, viscosity of water increases with decrease in temperature. So, viscosity of water at constant temperature is more in deep water as temperature is less in deep waters.