Answer the following questions: A. Sam leaves Venus in a spaceship to Mars and p
ID: 3160906 • Letter: A
Question
Answer the following questions:
A. Sam leaves Venus in a spaceship to Mars and passes Sally, who is on Earth, with a relative speed of 0.90c . They both measure the time for the voyage. Which of the statements below are true?
A. Sam measures the proper time.
B. Sally measure the proper time.
C. Sam’s measurement of the distance traveled is less.
D. Sally’s measurement of the distance traveled is less.
E. Both measure the same distance traveled.
F. Sally says the trip takes longer than Sam.
A, D, E
B, D, E
B, D, F
A, C, F
B. A long rod is constructed so that half of its length is made of lead and the other half is made of plastic. It can be rotated around either end. Which orientation will result in the greatest angular acceleration for the same torque?
rotation around lead end
rotation around plastic end
both the same
1.A, D, E
2.B, D, E
3.B, D, F
4.A, C, F
Explanation / Answer
According to the given problem,
A) Answer : 4
A, B, C, and F are all true. A duration measurement in a frame is proper time, and both Sam and Sally can take their own proper time measurements, for their own frames. So the closest they offer you is
B) Answer: 1
Angular acceleration a is related to torque (T) by this equation: a = T/I where I is the moment of inertia of the rod about a stated axis.
I = integral(r^2)dm where dm is an element of mass m at a radius r from the axis of rotation.
When the rod is rotated about an axis which is normal to the length of the rod, and at the plastic end, there will be a lot of mass (that of the lead) at a large radius, and I will be large. When the axis of rotation is at the lead end, the masses of elements of the lead part will be at a smaller radii, so I will be smaller.
Therefore a will be larger (with T constant) when the axis of rotation is at the lead end.
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