Physicsfan

But what makes the emit light when they are hot?

A block and tackle system of pulleys is used to raise a load of 500N through a height of 20m.the work done against friction is 2000J. what is the displacement of the effort and the mechanical advantage of the system?

since the displacement caused by the weighing machine is negligible,the force exerted by the machine on the ball(newtons third law) would be almost equal to the momentum of the ball when it hit the wighing machine, so that means the force exerted by the ball on the machine(weight) would be almost equal to its momentum. am i correct?

I think this is better. try potassium iodide paper. it is used as a chemical test for chlorine and nitrogen dioxide.

this is the diagram. sorry about the delay in reply

potassium iodide is present in iodine solution used in school laboratories as a test for starch content in leaves. (1.5g/100ml of water).It is also an additive in iodised salt.

if it was one 1 million light years away then light travelling from the star would take one million years to reach earth .if it exploded 2 million years ago.then the explosion would have been seen 1 million years ago......Right?

I already did that. but after that i cannot go further.the image is formed at a depth lower than the apparent deapth because when light travels from a denser to a rearer medium it bends away from normal and when the refracted ray is produced backward it meets with the ray travelling normal to the surface at a point above the actual position of object.how do i go further?

how do you derive that the refractive index of water with respect to air is real depth of an object placed in water/apparent depth as see from air?is this an approximation?