If the distance from earth to alpha centauri is 4.34 light-years, then a) alpha centauri is the closest star to earth. b) we see alpha centauri as it was four years ago. c) the distance is equal to 4.34 astronomical units. d) alpha centauri is four times farther from earth than the sun.

We see alpha centauri as it was 4.34 years ago.

work: w = fd (given)

work done by chet   =50*1 = 50 j

work done by mika =40*2 = 80 j

work done by sara =30*1.5 = 45 j

work done by bill =60*0.5 = 30 j

students in order from the greatest amount of work done to the least is mika> chet> sara> bill

hence option (b) is correct.

see the picture for the vector

the magnitude of the vector by pythagorean theorem

r = √( (-10)^2 + (3)^2 ) = √109

magnitude = √109 units

the direction angle between vector and x-axis is

tan^(-1)(3/10) = 16.699

so the direction is approximately 16.7 degrees north of west