Homework Set #2 Answers
Phys 1140, Fall 2008
Suggested readings: Taylor, pp 57-66. Beware: anywhere in Taylor you find something
described as a “provisional rule”, just ignore it. We won’t be using it in this course.
1) (9 points) Assume the errors in x and y are uncorrelated. For each example below,
w= x +y. Express w and w in standard format.
a) x = 13.1 +/- 0.8 m
y = 12.0 +/- 0.8 m
w = 25.1 +/- 1.1 m or w = 25 +/- 1 m
b) x = (3.0 +/- 0.2) x 10-4 kg m/s
y = (1.5 +/- 0.6) x 10-6 kg m/s
w = (3.0 +/- 0.2) x10-4 kg m/s
c) x = 8 +/- 1 V
y = 15 +/- 5 V
w = 23 +/- 5 V
2 (9 points) Assume the errors in x and y are uncorrelated. For each example below,
w= x -y. Express w and w in standard format.
a) x= 20.73 +/- 0.04 kg
y =40.196 +/- 0.008 kg
w = -19.47 +/- 0.04 kg
4
b) x = (6.4 +/- 0.5) x 10 m/s
y = (2.7 +/- 0.6) x 104 m/s
w = (3.7 +/- 0.8) x 104 m/s
c) x = 4250 +/- 500 m
y = 4320 +/- 900 m
w = 0 +/- 1000 m
3) (4 points) f(x) = 30 sin V
 = 1.00 +/- 0.04 radians.
f =?
f = |(df/d) cos (1.0) 0.04 V
= 0.6 V
4) (4 points) g(t) = e -3t A
t = 0.600 +/- 0.005
g =?
g = |(dg/dt) t| = |-3 e -1.8 0.005| A = 0.002 A (the unit
“A” means “Amp”.)