Please help me out guys!!

[Ahmed Khider]

I need the answer for this question before tomorrow...
Whats the difference between these 2 equations.
W=Fd Cos 0 and W=F Cos 0 d.
Keep in mind that W= Work, F= Force, d= Distance and 0 is the angle theta.

 

[Ahmed Khider]

badrobot14 Nibz CaptainDanger

 

[CaptainDanger]

Well if you put the values in either of the equation, you will get the same answer. I don't think there is any difference in them, if I don't have knowledge of something related to it then maybe I am wrong.

 

[Ahmed Khider]

Our teacher insists that there is some sort of difference between them.

 

[CaptainDanger]

In first case (W=Fd Cos 0) its displacement's x component which has to be used while in second case (W=F Cos 0 d) its force's x component.

 

[Ahmed Khider]

Mind if u elaborate more?

 

[CaptainDanger]

Do you have A levels book of Physics, the one endorsed by Cambridge?

 

[Ahmed Khider]

Nope..any idea where i can get it from or read it online?

 

[Nibz]

No, there is no difference in the two equations.
Use some common sense.

Take
F = 20
d = 10
θ = 45

And put these values in both equations.

W = Fd cos(45)
W = 20 x 10 x cos(45)
W = 141.4

W = F cos (45) d
W = 20 x cos(45) x 10
W = 141.4

If your teacher insists that both are different, kindly change your teacher.

 

[CaptainDanger]

Consider a force F acting along a line at an angle θ to the displacement, as shown in the above figure. The component of the force along the direction of the displacement is F cos θ.

Work done for displacement x = F cos θ × x
-------------------------------------= Fx cos θ

From the book. Forget about the displacement x component for now.