Answer both if you can, i need these
1. compare the effects of a solar and lunar eclipse.

2. what obstacles prevent scientists from sending humans to mars?

What are the phases shown in a and d called?

The 10-kg double wheel with radius of gyration of 125mm about o is connected to the spring of stiffness k = 600 n/m by a cord which is wrapped securely around the inner hub. if the wheel is released from rest on the incline with the spring stretched 225 mm, calculate the maximum velocity v of its center o during the ensuing motion. the wheel rolls without slipping

Four friends, a, b, c, and d are standing varying distances away from a speaker which is producing sound waves.