A crate is pushed across a horizontal floor at constant speed by a horizontal force of 140 N, which is just enough to overcome the friction between the crate and the floor. 

(a) How much work is done in pushing the crate through 10 m? 

(b) Rollers are then used under the crate to reduce friction and the same force is applied over the next 10 m. What happens to the work done now?
(c) Will there be any change in the speed of the crate?