Question

Light travels at 3.0 x 108 km/s. How far does light travel in 5 minutes? A) 1.5 x 1010 km B) 1.5 x 1011 km C) 9.0 x 109 km D) 9.0 x 1010 km

Answer 1

D) 9.0 x 10^10 km This is more an exercise in handling scientific notation than anything else. Since we have the distance that light travels in 1 second and we want to calculate how far it travels in 5 minutes, we must first calculate how many seconds are in 5 minutes. Simply multiplying 5 by 60 gives us 300 seconds. Now we need to multiply 300 by 3.0x10^8 km. So 300 * 3.0x10^8 = ? We could first convert 300 into scientific notion, but it's easier to just leave it along and assume that it's 300 x 10^0. So 300 times 3 is 900. And since 0 plus 8 is 8, we have as the answer: 900 x 10^8 But we're not done. The significand has to be greater than or equal to 1 and less than 10. So let's divide 900 by 100 and add 2 to the exponent. So we get 9 x 10^10 Finally, since our data had 2 significant figures, our result should have that as well. So let's add the 2nd digit getting: 9.0 x 10^10 So we know that light travels 9.0x10^10 km in 5 minutes, and that answer matches option "D" from the available choices.