Concept explainers
Owen and Dina are at rest in frame S.’ which is moving at 0.600c with respect to frame S. They play a game of catch while Ed. at rest in frame S, watches the action (Fig. P39.91). Owen throws the ball to Dina at 0.800c (according to Owen), and their separation (measured in S') is equal to 1.80 × 1012 m. (a) According to Dina, how fast is the ball moving? (b) According to Dina, what time interval is required for the ball to reach her? According to Ed, (c) how far apart are Owen and Dina, (d) how fast is the ball moving, and (e) what time interval is required for the ball to reach Dina?
(a)

The speed of ball according to Dina.
Answer to Problem 39.91CP
The speed of ball according to Dina is 0.800c.
Explanation of Solution
Given info: The frame S′ which is moving at 0.600c with respect to the frame S. The speed of ball is 0.800c with respect to Owen. The distance between Owen and Dina is 1.80×1012 m.
If both persons are in same frame then the velocity of ball will be same for both persons.
Owen and Dina are in same frame S and Owen throws the ball to the Dina with speed of 0.800c, then the speed of the ball with respect to the Dina is 0.800c.
Conclusion:
Therefore, the speed of ball according to Dina is 0.800c.
(b)

The time interval is required for the ball to reach Dina.
Answer to Problem 39.91CP
The time interval is required for the ball to reach Dina is 7.51×103 s.
Explanation of Solution
Given info: The frame S′ which is moving at 0.600c with respect to the frame S. The speed of ball is 0.800c with respect to Owen. The distance between Owen and Dina is 1.80×1012 m.
Write the expression for time taken by the ball to reach Dina.
t=LPu
Here,
t is the time taken by the ball.
LP is the distance between Owen and Dina.
u is the speed of the ball.
Substitute 0.800c for u and 1.80×1012 m for LP in above equation.
t=1.80×1012 m0.800c
The speed of the light is,
c=3.0×108 m/s
Substitute 3.0×108 m/s for c in above equation to find the time interval.
t=1.80×1012 m(0.800)(3.0×108 m/s)=7.51×103 s
Conclusion:
Therefore, the time interval is required for the ball to reach Dina is 7.51×103 s.
(c)

The distance between Owen and Dina with respect to Ed.
Answer to Problem 39.91CP
The distance between Owen and Dina with respect to Ed is 1.44×1012 m.
Explanation of Solution
Given info: The frame S′ which is moving at 0.600c with respect to the frame S. The speed of ball is 0.800c with respect to Owen. The distance between Owen and Dina is 1.80×1012 m.
Write the expression of distance between Owen and Dina with respect to the other frame S′.
L=LP√1−v2c2
Here,
L is the distance between Owen and Dina with respect to Ed.
v is the speed of frame S′.
Substitute 0.600c for v and 1.80×1012 m for LP in above equation.
L=(1.80×1012 m)√1−(0.600c)2c2=(1.80×1012 m)(0.8)=1.44×1012 m
Conclusion:
Therefore, the distance between Owen and Dina with respect to Ed is 1.44×1012 m.
(d)

The speed of the ball with respect to Ed.
Answer to Problem 39.91CP
The speed of the ball with respect to Ed is 0.385c.
Explanation of Solution
Given info: The frame S′ which is moving at 0.600c with respect to the frame S. The speed of ball is 0.800c with respect to Owen. The distance between Owen and Dina is 1.80×1012 m.
Write the expression of speed of the ball with respect to the other frame S′.
u′=u−v1−uvc2
Here,
u′ is the speed of ball with respect to Ed.
Substitute 0.600c for v and 0.800c for u in above equation.
u′=0.800c−0.600c1−(0.800c)(0.600c)c2=0.200c1−0.48=0.3846c≈0.385c
Conclusion:
Therefore, the speed of the ball with respect to Ed is 0.385c.
(e)

The time interval required for the ball to reach Dina with respect to Ed.
Answer to Problem 39.91CP
The time interval required for the ball to reach Dina with respect to Ed.
is 4.88×103 s.
Explanation of Solution
Given info: The frame S′ which is moving at 0.600c with respect to the frame S. The speed of ball is 0.800c with respect to Owen. The distance between Owen and Dina is 1.80×1012 m.
Write the expression for time taken by the ball to reach Dina with respect to Ed.
t′=γ(t−vLPc2) (1)
Here,
t′ is time taken by the ball to reach Dina with respect to Ed.
γ is the Lorentz factor.
Write the expression for the Lorentz factor.
γ=1√1−v2c2
Substitute 1√1−v2c2 for γ in equation (1).
t′=1√1−v2c2(t−vLPc2)
Substitute 0.600c for v, 3.0×108 m/s for c, 7.51×103 s for t and 1.80×1012 m for LP in above equation.
t′=1√1−(0.600c)2c2(7.51×103 s−(0.600c)(1.80×1012 m)c2)=1.25(7.51×103 s−1.08 m3.0×108 m/s)=4.88×103 s
Conclusion:
Therefore, the time interval required for the ball to reach Dina with respect to Ed.
is 4.88×103 s.
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Chapter 39 Solutions
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