Question 7. (20 points) sprin sale in an elevator. What will tlae scale read for

Question

Question 7. (20 points) sprin sale in an elevator. What will tlae scale read for tlhe woiglit of the person when a) the elovator is at rest? b) the elevator moves upward with constant speed of 4.2 m/s? c) the clevatoroves downward with constant speed of 1.2 m/s? d) the clevators upward with acceleration of 0.23g? e theelevator oves doward with acceleration of 0.23g? t) the elevator is in fre fall? Question 8. (20 points) A 65 kg hilker climbs to the top of a 4200 m-high mountain. The climb is made in 4.6 h starting at an elevation of 2800 m a) Calculate the work done by the hiker against gravity. b) Calculate the average power output in watts c) Calculate the average power output in horsepower Question 9. (20 points) In the system shown in the picture, suppose the coefticient of kinetic friction between mA and the plane is = 0.15, and that 7 1B-2.8 kg . Ignore masses of the (frictionless) pulley and the cord a) As m noves down, determine the magnitude of the acceleration of mA and B, given = 34° b) What snallest value of ill keep this system from accelerating?

Explanation / Answer

8 )

a )

using equation

Wgravity = m g ( D - d )

= 65 X 9.8 X ( 4200 - 2800 )

= 8.918 X 105 J

b )

t = 4.6

= 1.656 X 104 sec

using P = Wgravity / t

P = 8.918 X 105 / 1.656 X 104

P = 53.852 W

c )

we have 1 horse power = 746 Watts

1W = 1 / 746 = 0.00134 hp

so 53.852 W

= 53.852 X 0.00134

= 0.0721 hp

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