When traveling past an observer with a relative speed vv, a rocket is measured to be 9.10 mm long. When the rocket moves with a relative speed 2vv, its length is measured to be 4.90 mm. Required:
a. What is the speed v?
b. What is the proper length of the rocket?

Astone is thrown with a speed v0 and returns to earth, as the drawing shows. ignore friction and air resistance, and consider the initial and final locations of the stone. which one of the following correctly describes the change δpe in the gravitational potential energy and the change δke in the kinetic energy of the stone as it moves from its initial to its final location? options a.δpe = 0 j and δke = 0 j b.δpe is positive and δke is negative c.δpe = 0 j and δke is positive d.δpe is negative and δke is positive e.δpe = 0 j and δke is negative