Question

Light takes approximately 8 minutes to reach the earth from the Sun. The distance between earth and Sun in kilometers is __________.(speed of light=3x 108 ms-1)
A. $1440 \times {10^8}m$
B. $14 \times {10^8}m$
C. $140 \times {10^8}m$
D. $4 \times {10^8}m$

Answer 1

The speed of the light is defined as the distance covered by a body per unit of time, thus it is the ratio of distance covered by the body and the time taken by it. So, the distance between the earth and the sun is equal to the product of the velocity of light and the time taken by the light to reach from sun to earth.

Complete step by step answer:
$speed = \dfrac{{distance}}{{time}} \\\ \Rightarrow distance = speed \times time$
Where,
D is equal to the distance traveled by the particle or the body.
V is equal to the speed of that body (velocity if it has a certain direction)
T is equal to the time taken (usually in seconds by that body to travel that distance).
We know that speed of light is $3 \times {10^8}m/s$ and the time is given to be 8 minutes so the distance can be calculated as –
$d = 3 \times {10^8}m/s \times 8 \times 60 \\\ \therefore d = 1440 \times {10^8}m$

Hence option A is the correct answer.

Note: The standard unit for distance traveled is usually taken in “meters”, of time in “seconds” and that of speed in “meter/second”. The unit of time in the given question is minutes, so we have to convert it into seconds to get the right answer. We know that 1 minute is equal to 60 seconds, so 8 minutes is equal to 8 times 60 seconds. Here, the velocity of light which is equal $3 \times {10^8}m/s$ is considered as a universal constant and is usually denoted by “c”.