F1and F2constant forces acting
on the box as the box slides rightward across a frictionless floor. F1 is
horizontal with magnitude
2.0 N; F2is applied upward by 60oto the floor and has magnitude 4.0 N. The speed v of the box at certain instant is 3.0 m/s.
a)What is the power due to each force acting on the box at the instant and what is the net power? Is the net power changing at
b)If the magnitude of F2is, instead, 6.0 N, what
is the net power, and
is it changing?
Sample Problem 7-11
P1= F1v cos 180 = -6.0 W
P2= F2v cos 60= 6.0 W
→ K is const → v is const → Pnetis
P2= F2v cos 60= 9.0 W
W → Kisinc. → v is inc. → Pnetis changing.