x=4t？ Derive t to get v=8t, let N=av, substitute v= 10, and f=2 to get a= 1/5, so f=8/5t ∴t=5/8N.

Substitute x=4t? And get f=4/5 root x, and get the integral, W=∫ (4 0)4/5 root x dx = 8/15x3/2 | (40) =1

8/15 * 4 3/2-0 = 64/15 is what you want.

Note that v is speed, f is resistance and w is work.