Conservbation energy quesytion 1 You throw a 0.24-kilogram ball straight up. If

Question

Conservbation energy quesytion 1

You throw a 0.24-kilogram ball straight up. If the ball reaches a height of 56 cm, what is the work done on the ball by the gravitational force? You drop a 0.33-kilogram rock from a 21-meter high cliff. What is the work done on the rock by the gravitational force? Converting the energy of one food calorie into mechanical energy. how high could you lift a 152-lbs person? Converting the energy of one food calorie into mechanical energy. starting from rest, to what speed could you accelerate a 154-lbs person?

Explanation / Answer

a) workdone on the ball by graitational force is W= mgh downwards    = 0.24*0.56*9.8 = 1.3171 J

b) work done the rock is equal to the stored gravitational potential energy = 0.33*9.8*21 =67.971 J

c) energy of one food calorie is 1*10^3 cal ,, 1 cal = 4.18 J   ==> 1 food cal = 4.18*10^3 J = 4180 J

and mass of 152 lbs person =68.946 kg

                   now workdone tolift 68.946 kg person to a certain height is = mgh = 68.946*9.8*h = 4180 J

                                                                                   h = 4180/(68.946*9.8) = 6.184 m

d) 154 lbs = 69.85 kg, speed = ? , k.e = 4180 J, K.e = 1/2mv^2 = 4180 J,

                                                                                      v^2= 2*4180 / 69.85 = 119.68

       From equations of motioin v^2 - u^2 = 2as, v^2-0 = 2as

                                                                           s = v^2/ 2g

                                                                             = 119.68 / 2*9.8 = 6.160 m

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