# Chapter 30 - Worked Solutions

### to selected extension questions from the OUP text Senior Physics - Concepts in Context by Walding, Rapkins and Rossiter

My thanks to Peter Finch from St Joseph's College, Gregory Terrace, for these (pdf) solutions.

Solutions-Ch30-Finch.pdf

The rest are by me, Richard Walding:

Question 29
Yes (but the difference is very very small).

Question 30 Question 31
l = 5.80 m; v = 0.760 c
(a) l0 = 8.92 m long; no change to height
(b) t = 20.0 s
t = sv = 20 x 0.6499 = 13 s
(c) v is the same (0.760 c).

Question 32
l0 = 4 ly; t0 = 3 y; v = ? Question 33
t0 = 7 y; v = 0.8c; t = ?
(a) (b) Takes 11.67 y for signal travelling at c to reach Earth,
therefore total time = 9.336y + 11.67y = 21.0 y

Question 34
(a) EK = mc2 - m0c2 = c2(m - m0) = 9 x 1016 (20656 - 20000)
= 5.9 x 1019J

(b) EK (classical) = ½ mv2 = ½ x 20000 x (0.25 x 3 x 108)2
= 5.675 x 1019 J

D E = 2.75 x 1018 J
% difference = 2.75 x 1018 x 100 / 5.9 x 1019 = 4.7%

Question 35 v m (kg) 0.0 1.000 0.1 1.005 0.2 1.021 0.3 1.048 0.4 1.091 0.5 1.155 0.6 1.250 0.7 1.400 0.8 1.667 0.9 2.294 0.95 3.203 0.99 7.089 0.999 22.37 0.9999 70.71 Question 36
L0 = 6.00; v = 0.18c; your car L = ? Which is the length you measure his car to be.

Your car as measured by him is 6.15 m (ie L = 6.15 m) Which is what you measure your car to be.

Question 37
L0 = 4.225 ly; v = 0.80 c (a) v = L0/t
t = L0/v = 4.225/0.80 = 5.28 y

(b) (c) L = 2.535 ly Return to Physics Text Home Page