A 1kg block of ice at 10 degree C starts from rest and begins to slide down a sl

Question

A 1kg block of ice at 10 degree C starts from rest and begins to slide down a sloped roof It slides 6 m down the incline before falling off, as shown in the left-side figure, below. Because of uneven wear the frictional force on the ice increases as it moves down the roof, as shown in the graph on the right-side below. We want to use conservation of energy to find the speed with which it leaves the roof. Which of the following statements best describes the work done on the block of ice by various forces as it slides down the incline? Only friction does work on the block Gravity does positive work on the block and friction does negative work on the block Gravity does negative work on the block and friction does positive work on the block Both gravity and friction do negative work on the block Both gravity and friction do positive work on the block What is the magnitude of the total work done on the block by the frictional force? 9 J 12 J 6 J 2 J 4 J What mass of ice melts as it slides down the roof? (Consult your formula sheets for physical parameters for water/ice) 1.8 times 10^5 kg 2.1 times 10^-3 kg 3.4 times 10^-4 kg 2.7 times 10^-5 kg 3.6 times 10^-3 kg What is the total speed of the ice as it leaves the roof? 5.4 m/s 6.9 m/s 5.7 m/s

Explanation / Answer

1)both gravity and friction wil do negative work on the block--------------->D

2) work done by frictional force is area under the F vs x curve = 9 J--------------------->A

3) mass of ice melts during the slide is Q = m*L ==> m= Q/L = 9/334*10^3= 2.7*10^-5 kg--------------> D

4) total speed of the ice as it leaves the roof is 4.2 m/s           workdone = change in ke

                                                                     9 = 1/2 mv^2 => v= 18/1 => v= sqrt(18)= 3*sqrt2 = 3*1.41 = 4.242 m/s

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