An 8.0 kg block is released from rest, v1 = 0 m/s, on a rough incline, which has an angle of 40 from the horizontal. The block moves a distance of 1.6 m down the incline, in a time interval of 0.80 s, and acquires a velocity of v2 = 4.0 m/s.
The average rate at which friction force does work during the 0.80 s time interval is closest to:
a. +40 W
b. + 20 W
c. 0-
d. -40 W
e. -20 W