If we talk about cutoff then previous year cutoff for general category was 89.75 percentile.So you have prepare like that you can acheive this mark.

Here Is a link mentioned below by visiting that link you can know percentile vs marks and you can also know about marks vs ranks

https://engineering.careers360.com/articles/jee-main-marks-vs-percentile/amp

https://engineering.careers360.com/articles/jee-main-marks-vs-rank/amp

Now come to your second question if your fundamental are strong in physics then you should try a lot of problems from book called universal self scorer.you have select the chapters which you treat as easy and you have to work on that chapters only.if you are consistent during this one month period then definite you can score good in Physics.

Thanks

All the very best