Tag: physics

Questions Related to physics

Which of the following statements is NOT true for friction force?

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

  1. Friction force is produced when two objects rub against each other

  2. A lighter object will experience a smaller frictional force

  3. Friction produces more wear and tear

  4. Friction is harmful

Show answer
Correct Option: D
Explanation:

ADVANTAGES OF FRICTION
Friction plays a vital role in our daily life. Without friction we are handicap.
1. It is becomes difficult to walk on a slippery road due to low friction. When we move on ice, it     becomes difficult to walk due to low friction of ice.
2. We can not fix nail in the wood or wall if there is no friction. It is friction which holds the nail.
3. A horse can not pull a cart unless friction furnishes him a secure Foothold.
DISADVANTAGES OF FRICTION 
Despite the fact that the friction is very important in our daily life, it also has some disadvantages like:
1. The main disadvantage of friction is that it produces heat in various parts of machines. In this way     some useful energy is wasted as heat energy.
2. Due to friction we have to exert more power in machines.
3. It opposes the motion. 
4. Due to friction, noise is also produced in machines.
5. Due to friction, engines of automobiles consume more fuel which is a money loss.
So, Friction is useful for braking moving vehicles; for walking in smooth / slippery surfaces like snow and sand.
Answer (D) friction is harmful

You are marooned on a frictionless horizontal surface and cannot exert any horizontal force by pushing against the surface. How can you get off ?

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

  1. by jumping

  2. by spitting or sneezing

  3. by rolling your body on the surface

  4. by running on the plane

Show answer
Correct Option: B
Explanation:

By spitting or sneezing we can get off.

Since there is no friction present we need to spit or sneeze which will produce a suitable friction to get off. Also this will produce a momentum in opposite direction which will help us to move in opposite direcdtion.

Friction is a/an

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

  1. self-adjusting force

  2. necessary evil

  3. important force in daily life

  4. all the above

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Correct Option: D
Explanation:
  1. Static friction is considered a self adjusting force because it wants the object to remain at rest and not move. Therefore, if an external force is applied, the static force will be equal to the magnitude of external force, until it surpasses the threshold of the motion. Hence friction is a self-adjusting force.
  2. If there is no friction between any two surfaces in contact , then we will not be able to walk properly on the earth. Hence friction is necessary, But too much friction will reduce the efficiency of machines. Hence friction is a necessary evil.
  3. Friction allows us to hold anything, pick up anything , allows us to go anywhere . Same goes with riding a car or a bike. Thus friction is important force in our daily life.

Friction should always be avoid.

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

  3. Ambiguous

  4. Data insufficient

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Correct Option: B
Explanation:

The friction can be avoided when the contact surface is smooth. But for a rough contact surface, the friction opposes the motion. Thus the given statement is false.

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

  3. Ambiguous

  4. Data insufficient

Show answer
Correct Option: A
Explanation:

Friction is the force that resists motion when the surface of one object comes into contact with the surface of another. In a machine, friction reduces the mechanical advantage , or the ratio of output to input an automobile, for instance , uses one-quarter of its energy on reducing friction. Hence the efficiency of machine is reduced due to friction.

A sphere $S$ roll without slipping, moving with a constant speed on a plank $P.$ The fraction between the upper surface of $P$ and the sphere is sufficient to prevent slipping, while the lower surface of $P$ is smooth and rests on the ground. Initially, $P$ is fixed to the ground by a pin $N.$ If $N$ is suddenly removed:

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

  1. S will begin to slip on P

  2. P will begin to move back wards

  3. the speed of s will decrease, and its angular velocity will increase

  4. there will be no charge in the motion of S and P will still be at rest

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Correct Option: D

As an empty vessel is filled with water, its fundamental frequency

physics superposition of waves-2: stationary (standing) waves: vibrations of air columns determining wavelength and speed of sound resonance tube resonance and sonometer

  1. Increases

  2. Decreases

  3. Remains the same

  4. None of these

Show answer
Correct Option: A
Explanation:

   An empty vessel with a base is like a closed organ pipe , and fundamental frequency of a closed organ pipe is given by ,

       $n _{1}=v/4l$ ,
where $l=$ length of air column in pipe (height of pipe) ,
  from above we get,    
       $n _{1}\propto 1/l$ ,
when the empty vessel is filled with water , the length of air column $l$ in pipe decreases and therefore fundamental frequency $n _{1}$ increases as length of air column and fundamental frequency are inversely proportional to each other .

In Kundt's tube experiment the metallic rod executes 

physics stationary waves determining wavelength and speed of sound resonance tube resonance and sonometer

  1. transverse vibration.

  2. longitudinal vibrations.

  3. both.

  4. none of these

Show answer
Correct Option: B
Explanation:

In metallic rod longitudinal waves travels in vibrations.
Option "B" is correct. 

The frequency of a whistle is 200 Hz. It is approaching to stationary observer with a speed 1/3 the speed of sound. The frequency of sound as heard by the observer will be 

physics stationary waves determining wavelength and speed of sound resonance tube resonance and sonometer

  1. $450 Hz$

  2. $300 Hz$

  3. $400 Hz$

  4. $425 Hz$

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Correct Option: B

The amplitude of vibration of the particles of air through which a sound wave of intensity $2.0 \times 10 ^ { - 6 } \mathrm { Wm } ^ { - 2 }$ and frequency $1.0 kHz$ is passing - (Density of air = 1.2 $k g m ^ { - 3 }$  and speed of sound in air = 330 $m s ^ { - 1 }$ is)

physics stationary waves determining wavelength and speed of sound resonance tube resonance and sonometer

  1. $4.4 \times 10 ^ { - 8 } m$

  2. $1.6 \times 10 ^ { - 8 } m$

  3. $2.4 \times 10 ^ { - 6 } m$

  4. $1.8 \times 10 ^ { - 6 } m$

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Correct Option: B