GS02-1093 - Introduction to Medical Physics I Basic Interactions

Problem Set 1.1 Solutions

1. (J & C 1-1) A car accelerates at a rate of 5.0 km per hour per sec. Express this acceleration in m s-2.

2

3

secm39.1

sec 60min

min 60hr

kmm10

sechrkm0.5 =⋅⋅⋅⋅

2. (J & C 1-2) A current of 1.0 µA flows into a condenser of capacity 100 nF for 5.0 s. Calculate the potential difference between the plates of the condenser.

V 50V 100.5

secA 1C

C 1F V

F 10nF

AA 10

nF 100sec 5.0A0.1

9-

6

=×=

⋅⋅⋅⋅⋅

=

==

−

µµ

CIt

CQV

3. (J & C 1-3) A patient is given an x-ray exposure of 200 R. Calculate this exposure in C kg-1.

kgC1016.5

R kgC10 2.58 R 200 24- −×=⋅

×⋅

4. (J & C 1-4) After a full course of treatment, a tumor received a dose of 4000 rad. Express this dose in Gray, in MeV per g.

gMeV105.2

gMeV1025

eV 10MeV

g 10kg

J 106.1eV

Gy kgJ 1 Gy 40

Gy 40cGyGy10

radcGy 1 rad 4000

11

106319

2

×=

×=×

⋅⋅

⋅

=⋅⋅

−

−

5. (J & C 1-5) A source of 60Co has an activity of 1100 Ci. Express this activity in Bq.

Bq 1007.4CiBq103.7 Ci 1100 1310 ×=×⋅

6. A graduate student raises four lead bricks in a bucket (100 pounds) to a third floor window (25 feet) in 15 seconds. Calculate:

a. The work done in Joules

J 3396mkg

secJ1sec

mkg3396

ftm305.0ft 25

secm81.9

lbkg 0.454 lb 100

height g mass work

2

2

2

2

2

=⋅⋅

⋅⋅

=

⋅⋅⋅⋅=

××=

b. The power developed in Watts

W226JsecW1

sec 15J 3396

timework power

=

⋅⋅=

=

c. The power developed in horsepower

hp 303.0Whp0.00134 W226 =⋅

7. Your new Hummer gets 10 miles per gallon of gasoline. Calculate this amount in reciprocal acres. [Optional: With gasoline at $4.00 per gallon, how do you expect to pay for the gas on a graduate student stipend?]

1-10

2

3 acre 10720.1acreft560,43

ftgal48.7

mift5280

galmi10 ×=⋅⋅⋅

Note: URLs you might find useful are www.onlineconversion.com for conversion

factors and http://physics.nist.gov/cuu/Constants/ for physical constants.