physics

i understand that i posted questions like crazy but you have to understand i do try them out i use this website as a last resort and mainly to see what you think i should do. there are still a few i can't get.

An object whose height is 3.5 cm is at a distance of 8.5 cm from a spherical concave mirror. Its image is real and has a height of 11.2 cm. Calculate the radius of curvature of the mirror. i got this one the answer is .130 m
but the second part asks for the new Do and i have tried everything and i can't seem to get it with having the two unknowns.

also the one that asks for time...A laser beam enters a 12.5 cm thick glass window at an angle of 39° (from the normal). The index of refraction of the glass is 1.46. the angle from which the beam crosses through the glass is 25.5 deg from the normal. How long does it take the beam to pass through the plate?

i know you have to draw a diagram and what not but i just don't understand how you use the trig functions.

the only other one i can't get is the shadow one that goes as fallows...2.0- m-long vertical stick in air casts a shadow 1.8 m long. If the same stick is placed at 08:00hrs in air in a flat bottomed pool of salt water half the height of the stick, how long is the shadow on the floor of the pool? (For this pool, n = 1.56.)

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  1. <<.A laser beam enters a 12.5 cm thick glass window at an angle of 39° (from the normal). The index of refraction of the glass is 1.46. the angle from which the beam crosses through the glass is 25.5 deg from the normal. How long does it take the beam to pass through the plate? >>

    The speed of light through the glass is V = c/N = (3.00*10^10 cm/s)/1.46
    = 2.05*10^10 cm/s

    The distance the light travels thropugh the glass is

    D = 12.5/cos 25.5 = 13.85 cm

    Time = D/V

    I answered a problem about the length of a shadow a stick on a saltwater pool bottom previously. Look again.

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  2. Please make sure you DO NOT use a tutor's name in place of your own. It's a form of impersonation, and you can cause yourself problems by doing this.

    Thanks.

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    Writeacher
  3. You cannot find new Do unless position of new image or height of new image is given.

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  4. With regard to the length of the shadow at the bottom of a pool, I was calculating the distance of the end of the shadow from a point directly below the stick. The bottom end of the shadow is displaced the same as it is at the surface. The length of the shadow at the bottom of the pool is the same as it is at the surface: 1.8 m. This is because the rays that pass by the bottom and the top of the pool remain parallel.

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