Vector force& and Optic question

[lionely]

Log question

The diagram shows a log being pulled up an Earth slope from X to y.

How much work is done against friction, the answer I get is not among the 4 choices..

also the part messed up by the scanner says 1000N force due to friction

The diagram shows a boy doing homework. He has a difficulty reading his book under the small light bulb.

Draw a ray diagram to show the shadow produced by his head on the table. What difference would it make to the shadow if the light bulb were replaced by a long fluroescent bulb? Draw a diagram to illustrate this case.

my attempt...

the darker part is the umbra

and the strokes are the penumbra does that drawing make any sense?


Please respond.

 

[PeterO]

Log question

The diagram shows a log being pulled up an Earth slope from X to y.

How much work is done against friction, the answer I get is not among the 4 choices..

also the part messed up by the scanner says 1000N force due to friction

The diagram shows a boy doing homework. He has a difficulty reading his book under the small light bulb.

Draw a ray diagram to show the shadow produced by his head on the table. What difference would it make to the shadow if the light bulb were replaced by a long fluroescent bulb? Draw a diagram to illustrate this case.

my attempt...

the darker part is the umbra

and the strokes are the penumbra does that drawing make any sense?


Please respond.

"Log question

The diagram shows a log being pulled up an Earth slope from X to y.

How much work is done against friction, the answer I get is not among the 4 choices..

also the part messed up by the scanner says 1000N force due to friction"

The question also says the log was dragged 50m

If you oppose a 1000N force over a distance of 50m you certainly get one of the options.
Perhaps you were working out a total energy change brought about by dragging up the hill as well.

 

[lionely]

is it 50,000 J?

 

[PeterO]

Log question

The diagram shows a log being pulled up an Earth slope from X to y.

How much work is done against friction, the answer I get is not among the 4 choices..

also the part messed up by the scanner says 1000N force due to friction

The diagram shows a boy doing homework. He has a difficulty reading his book under the small light bulb.

Draw a ray diagram to show the shadow produced by his head on the table. What difference would it make to the shadow if the light bulb were replaced by a long fluroescent bulb? Draw a diagram to illustrate this case.

my attempt...

the darker part is the umbra

and the strokes are the penumbra does that drawing make any sense?


Please respond.

In short, the drawing does not make any sense.

Better look up umbra and Penumbra

http://en.wikipedia.org/wiki/Umbra

is a start, though most Physics texts have great diagrams.

 

[PeterO]

is it 50,000 J?

That sounds logical to me.

 

[lionely]

Okay thanks sir I'll try to redraw the diagram, I drew the diagram in a rush.

 

[PeterO]

Okay thanks sir I'll try to redraw the diagram, I drew the diagram in a rush.

Don't forget they said "replaced by a long fluroescent bulb".

That means it behaves like an array of globes perhaps 1m long.

 

[lionely]

I'm sorry I don't follow, what would be 1m long the shadow?

 

[PeterO]

I'm sorry I don't follow, what would be 1m long the shadow?

The light source.

Have you seen the long flourescent tubes they use in many businesses, schools and many home garages / basements - instead of a normal Globe light fitting.

http://en.wikipedia.org/wiki/Fluorescent_lamp