Question

answer this question asap​

Answer 1

Explanation:

Have Given :-

Time taken by the pebble to reach the surface of water = 20 seconds

acceleration (g) = 10 m/s²

Speed of sound (v) = 330 m/s

(i) Since the pebble is falling freely.

So, initial velocity of the pebble (u) = 0

From second law of motion,

$\sf \: h = ut + \frac{1}{2} g {t}^{2}$

$\sf \: h = 0 \times 20 + \frac{1}{ \cancel2} \times \cancel{10} \times {(20)}^{ 2}$

$\sf \: h = 0 + 5 \times 400$

$\sf \: h = 2000 \: m$

$\sf (ii) \: Time \: for \: pebble \: to \: fall \: down, t_1 =20 \: s$

Time for sound to travel from water surface to top of the well,

$\sf \: t_2 = \frac{ H}{v}$

$\sf \: t_2 = \frac{2000}{330}$

$\sf \: t_2 = 6.06 \: s$

Total time for echo to be heard,

$\sf \: t=t_1 + t_2$

$\sf \: t=20+6.1$

$\sf \: t= 26.1 s$

(C) Have Given :-

Thickness of the pencil = 1.4 mm

Zero error = + 0.02cm = + 0.2mm

Actual thickness = ?

Correct reading = observed reading − zero error

Correct reading = 1.4 – (+0.2)

Correct reading = 1.4 – 0.2

Correct reading = 1.2 mm

I hope it is helpful

Answer 2

Answer:

a change which is spontanius is called irreversible change.

eg: water flowing through river, revolution of earth

Explanation: