If the pathfinder sends a signal to Mars’ moon, Phobos, which is 2,600,000 meters above it, how long (in seconds) before it reflects back and is received by the pathfinder? Answer to two decimal places.

The answer is 4f======since electrostatic force is given by    we let f be the electrostatic force when  r = 1 m    if we let  denote the electrostatic force when the distance is decreased so that r = 0.5m, then    we established earlier that f = kq₁q₂. therefore    the force will now be 4f.

Blue light reflected from the ball enters human eyes.