This question hasn’t been clearly stated, so I have to guess what it means.
The solution probably makes use of the following equations:
I guess a and b are distances such that b-a=0.01m. (Not sure whether m is metres or miles. Assume metres since mass is metric. But this makes 0.01m=1cm, a very short distance. It would make more sense if it was km, so 0.01km=10 metres. But I’ve assumed m=metre.)
The equation relating acceleration x, distance and speed is:
v2²-v1²=2xs, where s is distance=b-a=0.01 and v1 and v2 are speeds.
From this acceleration x=(v2²-v1²)/0.02.
Mass=100kg. F=100x (Newton’s Law)=5000(v2²-v1²).