Question

an object is thrown straight up. which of the following is true abought the sign of workdone by the force of gravity on the object, while the object moves up and then down

Answer 1

Answer:

Upward: Negative

Downward: Positve

Explanation:

Let upward be positive

We want to find the work done on the object upwards.

The equation of work done due to gravity is

$f _{g}d \cos( \alpha )$

It is read as force of gravity times displacement times cos of the angle between the force and displacement.

Since gravity is happening down of the center of mass and the displacement is upwards, the angle is 180° so

$f_{g}d \cos(180)$

Cosine of 180 is -1

so

$- f_{g}d$

If we go downwards, the sign will be positive because cos(0)=1