Assist in the following physics question explain well, physics homework help

i. A particle is moving around in a circle and its position is given in polar coordinates as x = Rcosθ, and y = Rsinθ, where R is the radius of the circle, and θ is in radians. From these equations derive the equation for centripetal acceleration.

ii.An archer pulls back 0.75 m on a bow which has a stiffness of 200 N/m. The arrow weighs 50 g. What is the velocity of the arrow immediately after release?

iii.Two identical cars collide head on. Each car is traveling at 100 km/h.

The impact force on each car is the same as hitting a solid wall at:

(a) 100 km/h

(b) 200 km/h

(c) 150 km/h

(d) 50 km/h