how to solve it?

sir,if we apply,5 cos theeta=1,we find that costheeta=1/5,so how its value is 53 degree?.....sir tell me where i am wrong?sir baki ques to isse solve ho rhe hain?

WHY NOT 51?

But as per formula given by Sir, a = omega*v ;Omega is inversely proprtional to v then how both of them can increase at the same time ?