RIDDLE

Could someone explain the ans in b（i)

what is Newton 1 2 3 law ?

how to do question 28-30

method 1

how to calculate it ? question 9

I want to ask what is active transport ?

thank you sir

Could any one send me some physics question about force and motion or Newton 's law?

Hi,everyone I am a HongKonger I study physics in english . Now, I am learning force and motion but I forgot the concept of the normal reaction and weight , my teacher said I have to read the book to learn it again but I think the most important is `how to calculate the force ` I think those concept is useless . I want to ask is it useless for know the concept or good for know it? Also , I want to ask how to study physics effectively . （my English is suck ,there may be many grammar mistake,please forgive me)