Exam1-practice-Phys172-2011spring-solutions

# Exam1-practice-Phys172-2011spring-solutions - Problems 1-3...

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Problems 1-3 For the next four problems consider vectors in the diagram shown below, in which each division is equal to 1 m. Problem 1 (5 pts) What are the components of the vector a a ? A) <8, -1> m B) <9, 2> m C) <-1, 8> m D) <3, 4> m E) <4, 3> m Problem 2 (5 pts) What is the magnitude of the vector a a ? A) 8.06 m ( ) 2 2 8 1 + - = a a B) 9 m C) 8.21 m D) 8.32 m E) 5 m Problem 3 (5 pts) Which one of the following statements is true about vectors a a , b a , c a and d a ? A) 0 = + + + d c b a a a a a B) d c b a a a a a - = + C) b c a a a a = + D) b c a a a a + = E) c b a a a a = - x H a a b a c a d a

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Problems 4-5 A tennis ball of mass 57 g is served in horizontal direction along x -axis and initially flies at speed 60 mph. Problem 4 (5 pts) What is the initial magnitude of its momentum? A) 3420 kg . m/s B) 1.5 kg . m/s hour onds mile meters hour miles kg mv p sec 3600 1600 60 057 . 0 × × = a C) 1500 kg . m/s D) 3.42 kg . m/s E) 22.1 kg . m/s Problem 5 (5 pts) What is the magnitude of the x -component of this tennis ball after 1 second? (gravitational force on the ball is downwards in - z direction) A) 2.1 kg . m/s B) 3420 kg . m/s C) 1.5 kg . m/s, since there is no force component in horizontal direction momentum component in this direction cannot changing (momentum principle) D) 3900 kg . m/s E) 22.1 x y z 60 mph
Problem 6 (5 pts) An electron was accelerated to from a speed 0.9999 c , to 0.99999 c in 1 second ( c =3 × 10 8 m/s is the speed of light). What was the average force applied to an electron during that second? Assume unidirectional motion. Mass of an electron is 9 × 10 -31 kg. A) 4.1 × 10 -20 N B) 2.4 × 10 -26 N C) 3.8 × 10 -24 N D) 3.8 × 10 -20 N E) 1.6 × 10 -21 N s m kg c c kg mv p i / 10 91 . 1 9999 . 0 1 10 3 9999 . 0 10 9 20 2 8 31 × = - × × = = - - γ a s m kg p f / 10 04 . 6 20 × - a t p F Δ Δ = / a a ( ) N s s m kg s m kg F 20 20 20 10 13 . 4 1 / / 10 91 . 1 / 10 04 . 6 - - - × = × - × = a Problem 7 (5 pts) If an object moves at constant speed, you can irrefutably conclude that: A) The object may be interacting with other objects in the universe, but the net interaction is zero B) The object does not interact with anything in the universe C) The net interaction with other objects in universe may be not zero, but it is constant in time D) The object does not obey laws of physics E) There is no gravity acting on that object

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Problems 8-10 An object of mass 2 kg moves at a constant speed 0.5 m/s along a path as shown.
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## This note was uploaded on 04/23/2011 for the course PHYS 172 taught by Professor ? during the Spring '08 term at Purdue University-West Lafayette.

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Exam1-practice-Phys172-2011spring-solutions - Problems 1-3...

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