Work done by gravity on a load pushed horizontally

[Faiza]

Omg Read This I Dun Understand! Help

A man pushes a heavy load across a horizontal floor. What is the work done by gravity on the load?
a. The work depends on the weight of the load.
b. The work done by gravity is negative.
c. The work done by gravity is zero.
d. The work done by gravity is positive.

 

[Pyrrhus]

Remember Work is the scalar product of displacement and Force, so what's the angle between the displacement and the Force of Gravity (weight)?

 

[Faiza]

no i dun think so

 

[Faiza]

the work done by a constant force F on a particle is defined as the product of the component of the force in the direction of the particles displacement and the magnitude of the displacement. If F makes an angle theta with the displacement then the work done by f is W=Fdcos thetha
if thetha is 90 degress its zero?

 

[Faiza]

i checked the answer and its zero

 

[Faiza]

:{ lol i dun get it

 

[Pyrrhus]

no i dun think so

what you don't think?

$$\frac{dW}{d \vec{x}} = \vec{F}$$

$$dW = \vec{F} \cdot d \vec{x}$$

Scalar Product or Point Product

$$\vec{A} \cdot \vec{B} = | \vec{A}||\vec{B}|cos\theta$$

where $$\theta$$ is the angle between the two vectors.

 

[Pyrrhus]

the work done by a constant force F on a particle is defined as the product of the component of the force in the direction of the particles displacement and the magnitude of the displacement. If F makes an angle theta with the displacement then the work done by f is W=Fdcos thetha
if thetha is 90 degress its zero?

What's the cosine of 90 degrees?

 

[Faiza]

Cos(90)=0?

 

[Pyrrhus]

Cos(90)=0?

Yes, so the work done by Gravity is?

 

[Faiza]

Zero...... Lol