kkannan2 wrote:
Hi
RK84 -how are you so sure that 90 is the answer just by using 90+90+90+45? The way I did it was rule out choices (B) and (D), since they contradict the fact that A is faster than B (these would mean B is faster than A). Then, I was down to 90, 77, and 110 seconds as my 3 possible answer options. I was not sure how to go from there. I see based off of your reasoning that 315 seconds is a multiple of 90 (90*3.5=315), but I'm not sure how you're using this as reasoning to solve this problem.
KarishmaB - also struggling to see your reasoning a bit here. If you could elaborate a bit more on how to calculate the lap time for B beyond simply askin us to visualize the gap between A and B and how it changes, that would help.
It uses the concepts of ratios, time speed distance and circular motion.
When A and B start from the same point at the same time and move in the same direction around a circle, they meet for the first time when the faster covers exactly one lap more than the slower.
Since A has covered 4.5 laps when they meet, it means B has covered 3.5 laps in that time.
So ratio of their speeds is 4.5:3.5 = 9:7
Hence ratio of time taken by them to cover the same distance (say 1 lap) will be 7:9 (inverse of speed)
Since A takes 70 secs for 1 lap, B will take 90 secs.
You can check out Ratios, TSD and circular motion in my content for free on Sunday through Super Sundays. Details here:
https://youtu.be/gN_vlDpUflo