Tag: physics

Questions Related to physics

The efficiency of machine is reduced due to friction.

physics friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it friction: a necessary evil

  1. True

  2. False

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Correct Option: A
Explanation:

Yes, the statement is true.

Friction introduces losses and decreases efficiency since friction generates heat which is an energy that should be converted in movement. That energy in the form of heat is a loss. Also friction increases increases the wear and tear of a machine thereby decreasing its efficiency.

A coin flicked across a table will stop, because :

physics friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it friction: a necessary evil

  1. It is heavy

  2. No force is acting on it

  3. Earth attracts the coin

  4. Table exerts a frictional force

Show answer
Correct Option: D
Explanation:

According to the first law of motion a body will remain in the state of rest or of uniform motion until or unless compelled by an external force.

In this case the coin will stop because an external force is exerted in the form of frictional force by the table that opposes the motion of the flicked coin.

Hence, correct answer is option $D$

The application of decreasing friction includes :

physics friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it friction: a necessary evil

  1. Ball bearing used in moving parts of a machine

  2. The streamlined shape of an aircraft

  3. The layer of air between the hull of a hovecraft.

  4. None of these.

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Correct Option: A,B,C
Explanation:

The application of decreasing friction is
(i) Ball bearings used in moving parts of a machine.
(ii) The stream lines shape of an aircraft.
(iii) The layer of air between the hull of a hovecraft.

Which of the following are done to increase  friction?

physics friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it friction: a necessary evil

  1. Making groove in the shoes

  2. polishing rough surface

  3. using ball bearing in wheels

  4. Creating an air cushion

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Correct Option: A
Explanation:

Soles of shoes are grooved because the grooves increases the friction and gives the good grip to the person while walking with shoes

A bob's weight is measured by a spring balance. Its volume is $10 cm^3$. In vacuum it measures $80 g$. What does it weigh in water?

physics upthrust in fluids, archimedes' principle and floatation upthrust is equal to the weight of displaced liquid pressure in fluids buoyancy

  1. $70 g$

  2. $80 g$

  3. $90 g$

  4. $76 g$

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Correct Option: A
Explanation:

Weight of bob $= 80g/1000 N$ where $g$ is acceleration due to gravity

Weight of water displaced $= 10\times1\times g/1000 = 10g/1000 N$
Apparent weight$ = 80g/1000 - 10g/1000 = 70g/1000 N$
Weight measured $= 70/1000kg = 70 g$

Upthrust due to fluid equals

physics upthrust in fluids, archimedes' principle and floatation upthrust is equal to the weight of displaced liquid pressure in fluids buoyancy

  1. Volume of liquid displaced

  2. Mass of liquid displaced

  3. Weight of liquid displaced

  4. None of the above

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Correct Option: C
Explanation:

Upthrust equals weight of fluid displaced by the object.

A ship has volume of $1,50,000 m^3$. It submerges $10\%$ in water. Upthrust felt by it equals

physics upthrust in fluids, archimedes' principle and floatation upthrust is equal to the weight of displaced liquid pressure in fluids buoyancy

  1. $15 \times 10^6 N$

  2. $15 \times 10^7 N$

  3. $15 \times 10^8 N$

  4. $15 \times 10^5 N$

Show answer
Correct Option: B
Explanation:

Volume submerged$ = 15,000 m^3 $

Upthrust $= 15000m^3 \times 1000 kg/m^3 \times 10 m/s^2$
$=15 \times 10^7 N$

Consider a cylinder of height $h$ and Cross sectional area $A$ completely submerged in a fluid of density $\rho$. What is upthrust?

physics upthrust in fluids, archimedes' principle and floatation upthrust is equal to the weight of displaced liquid pressure in fluids buoyancy

  1. $Ah\rho g$

  2. $Ah\rho /g$

  3. $A\rho g$

  4. $Ah^2 \rho g$

Show answer
Correct Option: A
Explanation:

Upthrust = weight of fluid displaced

= Vol of fluid displaced x density of fluid x acc. due to gravity
$=Ah\rho g$

An object having relative density 0.56 is dropped in water. Will it float or sink in water?

physics upthrust in fluids, archimedes' principle and floatation upthrust is equal to the weight of displaced liquid pressure in fluids buoyancy

  1. Sink

  2. Float

  3. Depends on the density of water

  4. Unsure

Show answer
Correct Option: B
Explanation:

Explanation: the relative density of water is 1 and that of the object is less than 1. Thus the upthrust experienced by the object will be more than the weight of the object making it float on the surface of water.

A body of density equal to density of fluid is sinking at speed of $1 m/s$ at $t=0$. What is distance covered by object in $1s$? 

physics upthrust in fluids, archimedes' principle and floatation upthrust is equal to the weight of displaced liquid pressure in fluids buoyancy

  1. $0.5m$

  2. $1m$

  3. $0.75m$

  4. $0.875m$

Show answer
Correct Option: B
Explanation:

Upthrust = weight of the body since density of body equals density of fluid

Hence, Net force $= 0$ and acceleration$ = 0$
Distance = speed x time$ = 1m$