# Practice_Test_2_Answers - 1 Solutions to Practice test 2 1...

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1 Solutions to Practice test 2 1. Which of the following is a statement of the first law of motion? According the first law a net force is necessary to change the state of rest or of uniform motion of an object. This can be used to define a force. c. A force is necessary to change the state of rest or motion of an object. 2. Which of the following is an example where the net force is zero? b. An object moving with uniform speed along a straight line. 3. Which of the following is true about the second law of motion? a. A net force always produces acceleration. 4. A cement block of mass 5.2 kg is sitting on a floor. The magnitude and direction of the force exerted by the floor on the block is: The weight of the block = 5.2 kg × -9.8 ms -2 = -51 N. The floor applies an equal and opposite force upward. c. 51 N up 5. What is the magnitude and direction of the force exerted by the block in question 4 on the floor? d. 51 N down 6. A force F produces an acceleration of 2.0 m.s -2 on a particle of mass m. What force will produce the same acceleration on a mass m/4? F = 2m; Let F 1 be the force that produces the same acceleration on m/4. F = ma = 2m 1 2 4 4 m F F = = d. F/4

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2 7. A force produces an acceleration 2.0 m.s -2 on an object of mass 1.6 kg. What acceleration will the same force produce on a 400 g object? If F is the force acting on 1.6 kg producing an acceleration of 2 ms -2 , then: F = 1.6 kg × 2.0 ms -2 = 3.2 N The acceleration produced by 3.2 N on 400 g mass is: -2 3.2 8 ms 0.4 F N a m kg = = = a. 8 m.s -2 8. A 1000 kg car traveling at 72 km.h -1 is brought to rest in a distance of 20 m. The force applied by the brakes is: v o = 72 kmh -1 = 20 ms -1 , v f = 0, x = 20 m v f 2 = v o 2 + 2ax; 0 = 20 2 + 2a(20); a = -10 ms -2 F = ma = 1000 kg (-10 ms -2 ) = -10000 N d. –10000 N 9. What is the acceleration produced by a 2 N force on a mass of 50 g? -2 2 40 ms 0.05 F N a m kg = = = b. 40 m.s -2 10. A force F is applied to a mass M. If twice this force (2F) is applied to three times the mass (3M), the ratio of the acceleration of the smaller mass to the acceleration of the larger mass is: The acceleration produced by force F on mass M is: F a M = If a 1 is the acceleration produced by 2F on 3M, then: 1 1 2 2 2 3 3 3 3 2 F F a a M M a a = = = = a. 3 to 2
3 11. What is the weight of a person who has a mass 62 kg? W = mg = 62 x 9.8 = 607.6 N c. 607.6 N 12. What is the mass of an object that weighs 1100 N at the sea level? 2 1100 112.2 kg 9.8 F N m a ms - = = = d. 112.2 kg 13. What is the acceleration of a 0.1-kg object which is subjected to a force F = (-10 i + 5 j ) N? -2 10 N 5 N 10 N 5 N ( 100 50 )ms 0.1 kg 0.1 kg 0.1 kg F i j i j a i j m - + - = = = + = - + b. (-100 i + 50 j ) m.s -2 14. If a 10 kg mass is hung from the end of a string, the tension on the string is: The weight of the 10 kg = 10 × 9.8 = 98 N acting downward. The tension of the string acting up supports this weight. c.

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## This note was uploaded on 05/01/2011 for the course PHY 2048 taught by Professor George during the Fall '10 term at Edison State College.

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Practice_Test_2_Answers - 1 Solutions to Practice test 2 1...

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