A crate of books is to be put on a truck with the help of some planks sloping up at 33◦. The mass of the crate is 100 kg, and the coefficient of sliding friction between it and the planks is 0.4. You and your friends push horizontally with a force ~F . The acceleration of gravity is 9.81 m/s2 . Once the crate has started to move, how large must F be in order to keep the crate moving at constant speed? Answer in units of kN.