Question

Practice Problem 27.3 SOLUTION A spaceship flies past earth with a speed of 0.980c (about 2.97 x 10 m/s) relative to earth. A crew member on the spaceship measures its length, obtaining the value 400 m. What is the length measured by observers on earth? SET UP The length of the spaceship in the frame in which it is at rest (400 m) is a proper length in this frame, corresponding to lo in We want to find the length measured by observers on earth, who see the ship moving with speed u. SOLVE From the equation, に4 /1--(400 m) /1 _ (0.000,-= 56.4 m REFLECT To measure l, we need two observers because we have to observe the positions of the two ends of the spaceship simultaneously in the earth's reference frame. We could use two observers with synchronized clocks (Figure 1. These two observations are simultaneous in the earth's reference frame, but they are not simultaneous as seen by an observer in the spaceship. Part A Practice Problem: Suppose your car is 5.00 m long when it is sitting at rest in your driveway. How fast would it have to move for its length (as seen by someone at rest in the driveway) to be 2.80 m? Express your answer in meters per second to three significant figures. 828 400 Submit My Anewere Glve Up 0.990c Incorrect; Try Again; 4 attempts remaining; no points deducted Continue 01 02 oThe two observers on earth (S) must measure x2 and x1 simultaneously to otin the correct length-xa-x, in their fame of reference

Answer 1