A roller of radius

 A roller of radius (r) 300mm and weighing 2000N is to be pulled over a curb of height 150 mm by a horizontal force P applied to the end of a string would tightly around the circumstances of the roller moving over the curb. Find the magnitude P required to start the roller to move over the curb. What is the least force needed through the centre of the wheel to just turn the roller over the curb ?