To solve this problem, we are going to use a scientific/mathematics strategy called Dimensional Analysis.
40 miles / 1 hour * 5280 feet / 1 mile = 211200 feet / 1 hour
211200 feet / 1 hour * 1 hour / 60 minutes = 3520 feet/ 1 minute
3520 feet / 1 minute * 1 minute / 60 seconds = approximately 59 feet / 1 second
Jackrabbits travel approximately 59 feet per second, when rounded to the nearest whole number.