A skater is moving to the right on an ice surface with no friction. What net for

Question

A skater is moving to the right on an ice surface with no friction. What net force is needed to slow her down at a steady rate? a. A force applied to the right and increasing in strength. b. A force applied to the right and decreasing in strength. c. A force applied to the right at a constant strength. d. A force applied to the left and decreasing in strength. e. A force applied to the left at a constant strength. An object of mass 5.0 kg has an initial speed of 10 m/s. What is its speed after a work of +50 J has been done on it? a. 4.5 m/s c. 12 m/s d. 14 m/s e. 20 m/s

Explanation / Answer

to slow her down at a steady rate,we need to apply a force which is opposite to the motion

hence the answer is

e) A force applied to the left at a constant strength

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using work energy theorem

Work done by the net force = change in kinetic energy

W = Kf - Ki

50 = (0.5*m*vf^2)-(0.5*m*vi^2)

50 = (0.5*5*vf^2)-(0.5*5*10^2)

0.5*5*vf^2 = 50+(0.5*5*10^2) = 300

vf^2 = 300/(0.5*5) = 120

vf = sqrt(120) = 11 m/sec

so the answer is b) 11 m/s

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