What is a law which states energy cannot be created of destroyed only transferred

What is the earliest point in the universe that we can observe? why can’t we see back further than this?

What is the role of lenses in microscopy?

On a frictionless air track, a blue glider with mass 0.200 kg is moving to the right with a speed of 8.00 m/s. it strikes a red glider that has mass 0.600 kg and that is initially at rest. after the collision, the blue glider is moving to the left with a speed of 3.00 m/s.(a) what are the magnitude and direction of the velocity of the red glider after the collision? (b) is this collision elastic?