Tag: dynamics - explaining motion

Questions Related to dynamics - explaining motion

What is drag ?

physics dynamics - explaining motion air resistance fluid friction moving through fluids

  1. Frictional force offered by fluids

  2. Friction force offered by a solid surface

  3. Pulling a body over a surface

  4. None of these

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Correct Option: A
Explanation:

The other name for fluid friction is drag. It opposes the relative motion of any object in liquids or gases.

If we drop a cup of water on a plate and a cup of oil on another plate, water is seen to spread faster along diameter. This is an example related to:

physics dynamics - explaining motion air resistance fluid friction moving through fluids

  1. fluid friction

  2. rolling friction

  3. sliding friction

  4. static friction

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Correct Option: A
Explanation:

This example relates to fluid friction. Speed of spreading of a volume of liquid depends on the liquid friction.Friction offered by water is less as its density is less than oil.

 Fill in the blank.
Dynamic Fluid Friction is ______ the sliding friction of solids.
physics dynamics - explaining motion air resistance fluid friction moving through fluids

  1. higher than

  2. lower than

  3. same as

  4. higher than or equal to

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Correct Option: B
Explanation:

Dynamic Fluid Friction is lower than sliding friction of solids.

The deeper we go inside a flowing river, fluid friction:

physics dynamics - explaining motion air resistance fluid friction moving through fluids

  1. decreases

  2. increases

  3. remains same

  4. becomes zero

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Correct Option: B
Explanation:

Fluid friction increases with the depth of a flowing liquid.

Which of the following statements indicates advantage of fluid friction?

physics dynamics - explaining motion air resistance fluid friction moving through fluids

  1. Walking on road

  2. Rolling stone on carpet

  3. Lubricating machine parts

  4. None of the above

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Correct Option: C
Explanation:

Lubricating machine parts indicates advantage of fluid friction. This helps in lowering the friction and thus helps to keep parts of machinery in good condition for some time. 

Fill in the blank. 
Water offers _______ fluid friction as compared to honey. 
physics dynamics - explaining motion air resistance fluid friction moving through fluids

  1. higher

  2. lower

  3. same

  4. zero

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Correct Option: B
Explanation:

Water, having less density than honey, offers lower fluid friction as compared to honey.

Hailstones falling from atmosphere relates to:

physics dynamics - explaining motion air resistance fluid friction moving through fluids

  1. static friction

  2. rolling friction

  3. sliding friction

  4. fluid friction

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Correct Option: D
Explanation:

Hailstones falling from atmosphere is related to Fluid friction. Fluid friction occurs when there is resistance between particles in fluids or in gases.

Aeroplanes are streamlined to reduce friction.

physics dynamics - explaining motion air resistance fluid friction moving through fluids

  1. True

  2. False

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Correct Option: A
Explanation:

Fluid

Aeroplanes are streamlined to reduce:

physics dynamics - explaining motion air resistance fluid friction moving through fluids

  1. fluid friction.

  2. sliding friction.

  3. kinetic friction.

  4. limiting friction.

Show answer
Correct Option: A
Explanation:

Fluid friction occurs when a solid object travels through a liquid or gas. Aeroplanes are streamlined to reduce the fluid friction.

A spherical body of radius R consists of a fluid of constant density and is in equilibrium under its own gravity. If$ P(r)$ is the pressure at $r(r < R)$, then the correct option(s) is(are)?

physics dynamics - explaining motion air resistance fluid friction moving through fluids

  1. $P(r=0)=0$

  2. $\dfrac{P(r=3R/4)}{P(r=2R/3)}=\dfrac{63}{80}$

  3. $\dfrac{P(r=3R/5)}{P(r=2R/5)}=\dfrac{16}{21}$

  4. $\dfrac{P(r=R/2)}{P(r=R/3)}=\dfrac{20}{27}$

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Correct Option: B