Question

A basic physics question

Answer 1

1)

No,kinetic energy cannot be negative since its given by KE=mv²,mass cannot be negative and the square of speed cannot b negative.

2)

Yes,any force opposing motion or displacement does negative work. They are often referred to as resistive forces (friction,air resistance,drag...)

3)

Nope it does not, it just forces the object to move in a circular path known as a centripetal force. It can accelerate an object by changing it's direction but not it's speed.

4)

No it cannot,If an object is sliding on the table (assuming it is not an incline), then most probably that normal force cancels out the weights effect or assuming there is an incline, it cancels the weight's y component.

5)

$w = f.d.cos \alpha = f.d.cos90 = 0$

The work done is zero

6)

$w = f.d.cos \theta = f.d.cos0 = f.d$

The work is just the product of the magnitude of the force exerted and the displacement of the object.

7)

$0 < \theta < 90 \\ 1 < cos \theta < 0$

Work is decreasing but positive

8)

$\theta = 90 \\ cos \theta = cos90 = 0$

Work is zero

9)

$90 < \theta < 180 \\ 0 < cos \theta < - 1$

Work is negative