How much work did the movers do (horizontally) pushing a 156.4 kg crate 12.65m a

Question

How much work did the movers do (horizontally) pushing a 156.4 kg crate 12.65m across a rough floor without acceleration, if the coefficient of kinetic friction was 0.63? ______ How much work must be done to stop a 1,224kg car traveling at 21.6m/s? ______ A baseball (m = 0.1417g, traveling 33.11m/s moves a fielder's glove backward 0.21cm when the ball is caught. What was the average force exerted by the ball on the glove? _______ A spring has a spring stiffness constant, k, of 448N/m. How much must this spring be stretched to store 99.21J of potential energy? _______ A 8.88kg monkey swings from one branch to another 1.49m higher. What is the change in potential energy? _______ A novice skier, starting from rest, slides down a frictionless 35.0 degree incline whose vertical height is 193.53m. How fast is she going when she reaches the bottom? ______ The roller coaster shown in the picture below is dragged up to point 1 where it is released from rest. Assuming no friction. calculate the speed at point 2. (Height of point 1: 46.05m: height of point 2: 0m)

Explanation / Answer

Apply Newton second law to the crate

F- fk = ma

since a= 0

F = fk = uk mg

W = F d= fd = uk mg d = 0.63 ( 156.4) ( 9.8) (12.65) = 12215 J

(2)

from the work energy thorem

W= 1/2 mv^2

= 1/2 ( 1224) ( 21.6)^2

=285534.72 J

(3)

Fd = 1/2 mv^2

F = 1/2 mv^2/ d

= 0.5(0.1417* 10^-3) ( 33.11)^2/0.21 * 10^-2

=7.76 N

(4)

W= 1/2 k x^2

99.21 = 1/2( 448) ( x^2)

x= 0.665 m

As per guide lines I worked first four problems

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