Name: Examples of Non-contact Forces
Uploaded: 2019-07-19
Duration: 3 min 24 s
Description: Can two objects apply force on each other without coming in physical contact? Can you push a door without touching it? Let's explore in this video.

Question

A pebble is dropped freely in a well from its top. It takes $20 s$ for the pebble to reach the water surface in the well. Taking $g = 10 {ms}^{- 2}$ and speed of sound = $330 {ms}^{_1}$ , find the time taken when echo is heard after the pebble is dropped.

Accepted Answer

The initial velocity of the body $u = 0$

The acceleration of the body $a = 10 {ms}^{- 2}$

Speed of sound $330 {ms}^{- 1}$

The time taken $t = 20 s$

Applying the second equation of motion and substituting the values, we have,

$S = ut + \frac{1}{2} a t^{2} = 0 \times 20 + \frac{1}{2} \times 10 \times {(20)}^{2}$

Or $S = 5 \times 400 = 2000 m$

Hence, the depth of the surface of the well is $2000 m$ .

The time taken by the sound to cover this distance is $T = \frac{distance}{speed} = \frac{2000}{330} = 6.1 s$

The total time taken by echo from the instant , the pebble is dropped is the sum of time taken by the pebble to reach the surface of the water plus the time taken by the sound to cover the depth of the well i.e.

Total time = $20 + 6.1 = 26.6 \sec .$

A pebble is dropped freely in a well from its top. It takes $20 s$ for the pebble to reach the water surface in the well. Taking $g = 10 {ms}^{- 2}$ and speed of sound = $330 {ms}^{_1}$ , find the time taken when echo is heard after the pebble is dropped.

Important Questions on Laws of Motion

Learn and Prepare for any exam you want !

A pebble is dropped freely in a well from its top. It takes 20 s for the pebble to reach the water surface in the well. Taking g=10 ms-2and speed of sound = 330 ms_1, find the time taken when echo is heard after the pebble is dropped.

Important Questions on Laws of Motion

Learn and Prepare for any exam you want !

A pebble is dropped freely in a well from its top. It takes $20 s$ for the pebble to reach the water surface in the well. Taking $g = 10 {ms}^{- 2}$ and speed of sound = $330 {ms}^{_1}$ , find the time taken when echo is heard after the pebble is dropped.