there is a lamppost which is 40 m high.5 m infront of the post there is a metal plate which is 8 m long.

which angle of the plate with the verticle line will give the longest shadow?

 

Moved to homework help

 

 

please show your ideas and workings first - then members can show you right direction to take.

i dont have ANY idea how to start it.

My general suggestion to to sketch the set-up. That may help you see what to try.

i dont have ANY idea how to start it.

 

Have you taken any trigonometry yet?

Yes

But how can I determine the maximum value using trigonometry?

Plz help me with any clue

Can you think of how there would be no shadow at all? That might help get you started.

Yeah ,when the sheet will make 0 or 180 degree with the lamp light,there will be no shadow.

Yeah ,when the sheet will make 0 or 180 degree with the lamp light,there will be no shadow.

So what angle is that with respect to the vertical line? And what condition will maximize a shadow?

So what angle is that with respect to the vertical line? And what condition will maximize a shadow?

it is 7.125degree using trigonometry.

and it is in the opposite position .that is -7.125 degree

it is 7.125degree using trigonometry.

and it is in the opposite position .that is -7.125 degree

 

The negative of the angle isn't the opposite condition. What's the angle between the plate and the light beam that maximizes the shadow?

i cant get it.sorry.

i also tried much to get this angle

is it when the angle gets 90 degree?

is it when the angle gets 90 degree?

Yes.

90°? Did I wrongly interpret the problem?

 

(red = shadow; black = pole and plate (circle because of different angles, at least this is what I interpreted), yellow the light beam between post and plate when it's placed at about 45°, blue if it's placed at 0° with the vertical)

 

I didn't calculate it, but shouldn't it be 45°?

 

Edited January 22, 20169 yr by Function