A cheetah can run at top speed for only about 20 seconds. If an antelope is too far away for a cheetah to catch it in 20 seconds, the antelope is probably safe. Your friend claims an antelope running 60 feet per second will not be safe if the cheetah running at 90 feet per second is 650 feet behind it. Is your friend correct?
From the start, The cheetah runs 90t where t = number of seconds The antelope is 650 + 60t away. 90t = 650 + 60t 30t = 650 t = 21.67 seconds to catch up, but is limited to 20 seconds. So YES the antelope is safe....barely...
