Download App

Motion in a Straight Line — Physics STD 11 Science — Question

Rajasthan BoardEnglish MediumSTD 11 SciencePhysicsMotion in a Straight Line5 Marks
Question
An object falling through a fluid is observed to have acceleration given by a = g - bv where g = gravitational acceleration and b is constant. After a long time of release, it is observed to fall with constant speed. What must be the value of constant speed?
✓

Answer

Key concept: If a spherical body of radius r is dropped in a viscous fluid, it is first accelerated and then its acceleration becomes zero and it attains a constant velocity called terminal velocity.

According to the problem, acceleration of object is given by the relation

a = g - bv

When speed becomes constant acceleration $\text{a}=\frac{\text{dv}}{\text{dt}}=0$ (uniform motion).

where, g = gravitational acceleration

Clearly, from above equation as speed increases acceleration will decrease. At a certain speed say v0, acceleration will be zero and speed will remain constant.

Hence, $\text{a}=\text{g}-\text{bv}_0=0$

$\Rightarrow\text{v}_0=\frac{\text{g}}{\text{b}}$

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free

Explore more

More "5 Marks Questions" from Motion in a Straight Line→Motion in a Straight Line — all question types→Physics STD 11 Science question papers→Rajasthan Board STD 11 Science question papers→Rajasthan Board question paper generator→

Similar questions

We would like to make a vessel whose volume does not change with temperature (take a hint from the problem above). We can use brass and iron $\big(\beta_\text{ubrass}=6\times10^{-5}/\text{K and }\beta_\text{uiron}=3.55\times10^{-5}\text{K}\big)$ to create a volume of 100cc. How do you think you can achieve this.
→
A cubical metal block of edge 12cm floats in mercury with one fifth of the height inside the mercury. Water is poured till the surface of the block is just immersed in it. Find the height of the water column to be poured. Specific gravity of mercury = 13.6.
→
Shows a convex lens of focal length 12cm lying in a uniform magnetic field B of magnitude 1.2T parallel to its principal axis. A particle with charge 2.0 × 10-3C and mass 2.0 × 10-5 kg is projected perpendicular to the plane of the diagram with a speed of 4.8 ms-1. The particle moves along a circle with its centre on the principal axis at a distance of 18cm from the lens. Show that the image of the particle moves along a circle and find the radius of that circle.

→
We have 0.5g of hydrogen gas in a cubic chamber of size 3cm kept at NTP. The gas in the chamber is compressed keeping the temperature constant till a final pressure of 100atm. Is one justified in assuming the ideal gas law, in the final state? (Hydrogen molecules can be consider as spheres of radius 1 A).
→
Why a hollow shaft is stronger than a solid shaft made from the same and equal amounts of material?
→
1 gram of water at 373K is converted into steam at the same temperature. The volume of 1cm3 of water becomes 1671cm3 on boiling. Calculate change in internal energy of the system, if heat of vapourisation is 540cal g-1. Given standard atmospheric pressure is 1.013 × 10% Nm-2.
→
What is the kinetic theory of gases? Explain the hypothesis of this theory and point out its limitations.
→
The illuminance of a small area changes from 900 lumen/m2 to 400 lumen/m2 when it is shifted along its normal by 10cm. Assuming that it is illuminated by a point source placed on the normal, find the distance between the source and the area in the original position.
→
A thin prism of angle $6.0^\circ,\omega=0.07$ and $\mu_\text{y}=1.50$ is combined with another thin prism having $\omega=0.08$ and $\mu_\text{y}=1.60.$ The combination produces no deviation in the mean ray.
  1. Find the angle of the second prism.
  2. Find the net angular dispersion produced by the combination when a beam of white light passes through it.
  3. If the prisms are similarly directed, what will be the deviation in the mean ray
  4. Find the angular dispersion in the situation described in (c).
→
i. Pick out only the vector quantities from the following: Temperature, pressure, impulse, time, power, charge.
ii. Show by drawing a neat diagram that the flight of a bird is an example of composition of vectors.
iii. A man is travelling at $10.8 km h ^{-1}$ in a topless car on a rainy day. He holds his umbrella at an angle $37^{\circ}$ to the vertical to protect himself from the rain which is falling vertically downwards. What is the velocity of the rain? $\left[\right.$ Given $\cos 37^{\circ}=\frac{4}{5}$ ]
→