Radar can be used to measure the distance from the sun to the earth.

a) the speed of the wave is 3x10^8 m/s and the distance to the sun is 1.496x10^8 km; how long should the signal take to reach the sun and come back?
b) why can’t sound waves be used in this situation?

1)  t = 16.6 minutes

2)  Sound waves need a medium for propagation.

Explanation:

Given,

The speed of the wave, v = 3 x 10⁸ m/s

The distance between Sun and the Earth, d = 1.496 x 10⁸ Km

                                                                         = 1.496 x 10¹¹ m

The speed and distance is given by the formula

                                             v = d/t

Or,                                        t = d / v

Substituting the values in the above equation

                                             t = 1.496 x 10¹¹ m / 3 x 10⁸ m/s

                                               = 498.67 s

                                              = 8.3 minutes

Since the radar requires the signals to come back. Therefore, the total distance the waves traveled is twice the distance between the Sun and the Earth.

The time taken by the waves to reach radar is

                                        t = 2 x 8.3 min

                                          = 16.6 min

Hence, time taken by the signal take to reach the sun and come back is, t = 16.6 min

The light waves do not require a medium for propagation. But the sound waves need a medium such as air, water, metal, or atmosphere for the propagation.

A vacuum exists beyond the outer space of the Earth's atmosphere. No mediums exist there.  

So, sound waves can't be used in this situation.

answer: 802.3 kilo joules of energy represents 191.75 kilo calorie of energy.

explanation:

energy released during combustion of one mole methane = 802.3 kilo joules

if 1 kilo joule = 0.239006   kilo calorie

then ,802.3 kilo joule will be = 802.30.239006 kilo calorie

802.3 kilo joule = 191.75 kilo calorie

hence, the energy in kilo calorie is 191.75 kilo calorie.