Physics Review Question Unit: Mechanics Year: 1993 Question#: 10 Question: A bird feeder with two birds has a total mass of 2.0 kilograms and is supported by wire as shown in the diagram below. The Force in the top wire is approximately (1 ) 10. N (2 ) 14 N (3 ) 20. N (4 ) 39 N What is this question really asking? Explanation by: Jessica S [ Return to question menu ] Answer 1 10. N INCORRECT The mass of the bird feeder is 2 kg. To find the force applied in the top wire, we use the formula F = ma (force = mass x accelertion due to gravity). Substituting the known values (mass and acceleration due to gravity), we get F = 2.0 kg x 9.8 m/s2; F is approximately equal to 20 N. 10 N is not equal to 20 N; therefore, answer 1 is incorrect. return to top Answer 2 14 N INCORRECT The mass of the bird feeder is 2 kg. To find the force applied in the top wire, we use the formula F = ma (force = mass x accelertion due to gravity). Substituting the known values (mass and acceleration due to gravity), we get F = 2.0 kg x 9.8 m/s2; F is approximately equal to 20 N. 14 N is not equal to 20 N; therefore, answer 2 is incorrect. return to top Answer 3 20. N CORRECT The mass of the bird feeder is 2 kg. To find the force applied in the top wire, we use the formula F = ma (force = mass x accelertion due to gravity). Substituting the known values (mass and acceleration due to gravity), we get F = 2.0 kg x 9.8 m/s2; F is approximately equal to 20 N. Answer 3 is correct. return to top Answer 4 39 N INCORRECT The mass of the bird feeder is 2 kg. To find the force applied in the top wire, we use the formula F = ma (force = mass x accelertion due to gravity). Substituting the known values (mass and acceleration due to gravity), we get F = 2.0 kg x 9.8 m/s2; F is approximately equal to 20 N. 39 N is not equal to 20 N; therefore, answer 4 is incorrect. return to top What's this question really asking? This question is testing your ability to sort through information and to pick out what is needed; and the ability to plug values into the correct formula. The two birds, and the two angles are red herrings trying to confuse you. Don't get confused! All you need is the mass of the object, to plug into the equation w = mg. return to top This web site is designed and maintained by Science Joy Wagon and may not be reproduced or redistributed without written permission from Science Joy Wagon. Contact with comments.