Physics 3650 Quiz 1 October 1, 009 Name SOLUTION 1. If the displacement of the object, x, is related to velocity, v, according to the relation x = A v, the constant, A, has the dimension of which of the following? a. Acceleration. b. Length. c. Time. d. Area... If you exert a force F on an object, the force which the object exerts on you will a. Depend on whether or not the object is moving. b. Depend on whether or not you are moving. c. Depend on the relative masses of you and the object. d. Always be F. 3. What is the SI unit of momentum? a. N m. b. N/s. c. N s. d. N/m.
Physics 3650 Quiz October 19, 009 Name SOLUTION 1. Astronauts in a spaceship traveling at V = 0.600c relative Earth sign off from space control saying that they are going to nap for 1 hour and then call back. t 0 1.00 h t = t 0 /(1-v /c ) 1/ a. How long does their nap last as measured on Earth? t = 1.00 s /(1-(0.600c) /c ) 1/ = 1.5 h Astronauts b. Who measures the proper time of the nap?. A stick that has a proper length of 1.00 m moves in a direction along its length with speed V relative to you. The length of the stick as measured by you is 0.91 m. What is the speed V? L = 0.91 m, L 0 = 1.00 m L = L 0 (1-v /c ) 1/ L/ L 0 = (1-v /c ) 1/ (L/ L 0 ) = (1-v /c ) v /c = 1 - (L/ L 0 )
v = 0.06c Physics 3650 Quiz 3 October 1, 009 Name SOLUTION 1. Spaceship R is moving to the right at a speed of 0.700c with respect to Earth. A second spaceship, L, moves to the left at the speed of 0.300c with respect to Earth. What is the speed of L with respect to R? V RE = 0.700c V LE = - 0.300c V LR =? V LR VLE V V V 1 c ER LE ER 0.300c 0.700c V SA 0. 86c ( 0.300c) ( 0.700c) 1 c Physics 3650 Quiz October 6, 009 Name SOLUTION
1. A sodium surface is illuminated with light of wavelength 0.300 m. The work function for sodium is.6 ev. Find a. The maximum kinetic energy of the ejected photoelectrons. K max hc/ - W 0 K max (10 ev-nm)/nm - (.6 ev) = 1.67 ev b. The cutoff wavelength for sodium. W 0 = hc/ 0 0 =(10 ev-nm)/.6 ev = 50 nm Physics 3650 Quiz 5 October 8, 009 Name SOLUTION An X-ray photon of wavelength 5.00 pm that collides with an electron is scattered by an angle of 60.0 o. a. What is the change in wavelength of the photon? = h/(m e c)(1-cos()) (.3 x 10-1 m)(1-cos(60.0 o )) = 0.001 nm b. What is the kinetic energy of the scattered electron? E = hc/ = (10 ev-nm)/(0.00500 nm) = 8 kev 0.00500 nm + 0.001 nm = 0.006 nm
E = hc/ = (10 ev-nm)/(0.006 nm) = 199 kev K = E E = 9.0 kev c. What is the magnitude of the scattered photon s momentum? p = h/ p = (6.63 x 10-3 J-s)/(0.006 x 10-9 m) = 1.066 x 10 - kg-m/s Physics 3650 Quiz 6 November 6, 009 Name _SOLUTION A hydrogen atom is in its second excited state according to the Borh model (n = 3). a. What is the radius of the Bohr orbit? r n = n a 0 r 5 = (3) (0.059 nm) = 0.76 nm L n = n h/() b. What is the angular momentum of the electron? L 5 =3 h/() = 3.17 x 10-3 J-s L = p r c. What is the electron s kinetic energy?
p = L/r = 6.65 x 10-5 kg-m/s K = p /(m e ) = (6.65 x 10-5 kg-m/s) /((9.11 x 10-31 kg)) =.3 x 10-19 J = 1.5 ev Alternatively: E 3 = - (13.6 ev)/3 = -1.51 ev K 3 = E 3 = 1.51 ev d. As the electron jumps to the ground state, what is the energy of the emitted photon? hf = E 3 E 1 = -1.51 ev (-13.6 ev) = 1.09 ev hc/ = 1.09 ev = 103 nm e. What is the wavelength of the emitted photon? Physics 3650 Quiz 7 November 18, 009 Name SOLUTION 1. Estimate the radius of the following nuclei: a. 7 3Li, r = (1.0 x 10-15 m) A 1/3 = (1.0 x 10-15 m) 7 1/3 =.9 x 10-15 m b. 09 83Bi.
r = (1.0 x 10-15 m) A 1/3 = (1.0 x 10-15 m) 09 1/3 = 7.11 x 10-15 m. There is a limit to the size of a stable nucleus because of a. The limited range of the strong nuclear force. b. The weakness of the electrostatic force. c. The weakness of the gravitational force. d. None of the given answers. Physics 3650 Quiz 8 November 0, 009 Name _SOLUTION A certain radioactive nucleus has a half life of 00 s. A sample containing this isotope has an initial activity of 80,000 Bq. a. What is the decay constant? = ln () / T 1/ = ln()/(00 s) = 0.00366 1/s b. How many nuclei were there initially? R o = N o N o = R o / = (80,000 Bq) /(0.00366 1/s) =.31 x 10 7 c. What is the activity of this sample 10.0 minutes later? R = R o e - t = (80,000)e -0.00366 1/s (600 s) = 10,000 Bq
Physics 3650 Quiz 9 November 3, 009 Name SOLUTION The mass of 56 Fe is 55.93 9 u and the mass of 56 Co is 55.939 9 u.. a. Which isotope decays into the other and by what process? Write the equation for the decay. Cobalt-56 decays into Iron-56 by beta decay. (Just compare the masses.) 56 7 Co 56 6 Fe e b. How much energy is released in the process? m = m i mf = 55.9399 u 55.939 u = 0.00500 u E = m c = (0.00500)(931.5 Mev/c ) c =.66 MeV Physics 3650 Quiz 10 December, 009 Name SOLUTION Two of the naturally occurring radioactive decay sequences start with 3 Th, 35 9 90 and U. The first five decays of these two sequences are:,,,, and
,,,,. 3 a. Determine the resulting intermediate daughter nuclei in case of 90Th, and 8 90Th 88Ra 3 8 88 8 89 Ra Ac 8 89 8 90 Ac e Th e 90Th 88Ra 8 0 88Ra 86Rn 35 b. work out the 9U. sequence. 31 9U 90Th 35 31 90 Th 31 Pa e 91 0 91Pa 89Ac 31 0 89 Ac 0 90 Th e 16 90Th 88Ra 0.