# Thread: need assistance on word problem

1. ## need assistance on word problem

problem

light travels at a speed of about 300,000 kilometers per second. the distance that light travels in one year is called a light year. the star alpha Centauri is 4.34 light years from earth. how many years would it take a rocket traveling at 6000 kilometers per hour to reach alpha Centauri? solve this problem, and explain how you use the meaning of multiplication and division in solving it.

what i tried

use division for 300,000/6000 kilometers=50 years for the rocket to reach alpha Centauri.

2. ## Re: need assistance on word problem

Green11

a light year is the distance that light travels in one year
this distance is aprox...300000km x 3600 seconds x 24 hours X365 days.....
after you compute all this multiply it by 4.34 and you have the distance in Km betwen the Earth and A-Centauri...
Now divide that distance by the 6000 Km your rocket is travelling and you will find the minutes needed ...then convert them to years...
the result will surpise you !!!
good luck with the calculations

3. ## Re: need assistance on word problem

No, that's completely wrong. One thing wrong- and a key to the main problem- is that you give units of "km" for the "6000", which is incorrect because it should be "km/hr", and do NOT give units for the speed of light. Had you done so, you would have realized that you were dividing "km/sec" by "km/hour" which, since dividing by a fraction, is the same inverting the fraction, is $\frac{km}{sec}\frac{hr}{km}= \frac{hr}{sec}$. Of course, your answer should be time, either seconds or hours, not "hr/sec".

Also you did not use all three pieces of information! You use that the speed of light is "300000 km/sec" and that the speed of the spaceship is 6000 km/hr, but you have NOT used the fact that the distance is to be "4.34 light years.

You are given those three pieces of information- in units of "km/sec", "6000 km/hr" and "light years" and want a "time" answer- in either seconds or hours. We can get time from a speed, in "km/hour", and a distance, in "km", by a division: (km)(hour/km)= hours but you do not have a distance in km. You have, instead, a distance in "light years". You are told two things- that light travels at 300000 km/sec and that one light year is the distance light travels in a year. So how many km will light travel in a minute? in an hour? in a day? in a year? That is, how many km are there in one light year? That is the information you need so you can find the distance to alpha Centauri in kilometers and then determine the time required at 6000 km/hour. (It is a heck of a lot more than 50 hours!)