Hi, i have a WEP related question regarding mixing work and energy
So here it is (i came up with it and i dont quite understand the work done by applied force)
A box is on an inclined plane and it is pushed down. at its final position Y, it has a speed of 1m/s. the distance covered on the plane is 5m, the total resistive force is 200N and the mass of the box is 20kg. the distance vertically upwards to the original box position X, is 3m
1) find the KE at X.(this one is self explainatory)
KE=1/2 x 20 x 1^2= 10J
2) What is the work done by gravity
WD by gravity= mgh=20 x 10 x 3 = 600J
3) what is the work done against resistive forces?
WD against resistive forces=200 x 5=1000J
4) what is the applied force?
(this part i dont understand, usually WD by applied force is Applied Force X Distance Covered. But in this case we dont have the applied force. in another example that i did once, the box was moving upwards so the equation is
WD by applied force= WD against resistive +KE+WD against gravity
But now im not very sure if i should plus the work done by gravity. This is what im thinking
WD by applied force= WD against resistive + KE [im thinking this as WD by gravity is done BY gravity so it should not include in this? however im also thinking like this
WD by applied force= WD against resistive+KE +WD by gravity [im thinking like this as at 3m high it has a GPE of 600J
But in the second case if wat im thinking is true it gets even more complicated for me as i thought WD by gravity is a loss in GPE, so pls ecplain these parts to me. Thanks so much for the help
WD by gravity + WD by applied force = WD against resistive forces + KE
1) find the KE at X.
0J (at starting position, no speed at all)
2) What is the work done by gravity
WD by gravity= mgh=20 x 10 x 3 = 600J
3) what is the work done against resistive forces? (resistive force - friction)
G.P.E at X = K.E at Y + W.D against friction
600 = 10 + W.D against friction
W.D against friction = 690J
4) what is the applied force? (assuming the box travels at constant speed)
200N