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

Which of the following statements indicates advantage of fluid friction?

  1. Walking on road

  2. Rolling stone on carpet

  3. Lubricating machine parts

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
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. 

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

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)?

  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. $\dfrac{P(r=R/2)}{P(r=R/3)}=\dfrac{20}{27}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For a fluid sphere under gravity, the pressure distribution follows hydrostatic equilibrium. Calculating the ratio of pressures at the specified radii confirms the result in option B.

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

Mr. Verma (50 kg) and Mr. mathur (60 kg) are sitting at the two extreames of 4 m long boat (40 kg) standing still in water. to discuss a mechanics problem, they come the middle of the boat . neglecting friction with water, how far does the boat move in the water during the process?

  1. $1.33 m$

  2. $2 m$

  3. $10 m$

  4. $1 m$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Using the center of mass principle, the initial center of mass of the system (men + boat) is at a certain position. When they move to the center, the boat must shift to keep the center of mass stationary because there are no external horizontal forces.

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

The arrow with a pointed tip can move faster in air than that of with a blunt tip.

  1. True

  2. False

  3. Ambiguous

  4. Data insufficient
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A pointed tip is more sharper than a blunt tip. So the air resistance for the pointed tip is less than that of the blunt tip. Since the air resistance opposes the motion, so the pointed can tip move faster than that of blunt tip. Thus, the given statement is true.