Tag: physics

Quizzes (598) Questions (13441)

Questions Related to physics

Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

A boy clapped his hands near a cliff and heard the echo after 4s. What is the distance of the cliff from the person if the speed of the sound, v is taken as 346 ms$^{-1}$?

  1. 2 m

  2. 1384 m

  3. 692 m

  4. 2768 m
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Given, Speed of sound, $v = 346 ms^{-1}$ Time taken for hearing the echo, $t = 4 s$
Distance travelled by the sound $ = v \times t = 346 m/s \times 4 s = 1384 m$
In 4 s sound has to travel twice the distance between the cliff and the person.
Hence, the distance between the cliff and the person $= 1384 m/2 = 692 m$

Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

A sound wave of wavelength $\lambda$ travels towards the right horizontally with a velocity V. It strikes and reflects from a vertical plane surface, travelling at a speed v towards the left. The number of positive crests striking during a time interval of three seconds on the wall is :

  1. $3(V+v)/\lambda$

  2. $3(V-v)/\lambda$

  3. $(V+v)/3\lambda$

  4. $(V-v)/3\lambda$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The relative velocity of the wave crests with respect to the wall is (V+v). The distance covered by the crests in time t is (V+v)t. The number of crests is distance / wavelength = (V+v)t / lambda. For t=3s, this is 3(V+v)/lambda.

Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

A person is in front of a fort wall.  The person can hear an echo of sound produced by him when minimum distance between person and wall is 16.75 m. The velocity of sound in air is:

  1. 330 m/s

  2. 335 m/s

  3. 337.5 m/s

  4. 345 m/s
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Minimum time for echo is $0.15$
So, distance travelled for echo is $=2\times 16.75=$ speed of sound $\times$ minimum time for echo
$\Rightarrow 2\times 16.75=\vartheta _{s}\times 0.1$

$\Rightarrow \vartheta _{s}=\dfrac{2\times 16.75}{0.1}$$=335 m/s$

Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

A boy shouts while standing in front of a hill. He hears an echo after 6 sec. If the speed of sound  in air is 340 m/s. What is the distance of the hill from the position of the body?

  1. 519 m

  2. 1020 m

  3. 2040 m

  4. none
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let distance of hill from the position of the body = d
Echo is heard after 6 sec
$d = v \dfrac{t}{2}$
$= \dfrac{(340 \times 6)}{2}$
$= 1020 m$

Multiple choice physics study of sound determination of speed of sound by echo problems on sound sound needs a medium

A sonar echo takes 8.8 s to return from a shack. How far away is the shack?

Given speed of sound in sea-water = 1533 m/s

  1. 348 m

  2. 5720 m

  3. 6745 m

  4. 13490 m
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let $d$ be the distance of shack from the sonar . Therefore  distance covered by sound to come back to sonar after reflection from shack ,  $=d$ ,

given , speed of sound in sea water $v=1533m/s  ,  t=8.8s$ ,
we have , distance=speed$\times time$ ,
               $d=v\times t=1533\times8.8$ ,
or            $d=13490.4m$

Multiple choice physics turning on a pivot the turning effect of a force moment of force or torque turning effect of force couple

While opening a tap with two fingers, the forces applied are  

  1. equal in magnitude

  2. parallel to each other

  3. opposite in direction

  4. All of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

While opening a tap with two fingers, a couple should be applied which is defined as a pair of parallel equal forces acting in opposite direction about two different axis.

Multiple choice physics turning on a pivot the turning effect of a force moment of force or torque turning effect of force couple

On applying a constant torque on a body-

  1. linear velocity increases

  2. angular velocity changes

  3. it will rotate with constant angular velocity

  4. it will move with constant velocity
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A constant torque applied to a rigid body results in constant angular acceleration, which causes the angular velocity to change over time.