Question

4. A stone of weight 2 kgf is lying on the roof of
a building 60 m high. Calculate the amount of
stored energy in the stone. [Take 1 kgf = 10 NI
[1200 J]
5. A stone of weight 0.25 kgf is projected vertically
upward such that it attains a height of 40 m.
Calculate the amount of energy in the stone at
the highest point. (Take 1 kgf = 10 N] [100 J]
6. A boy of mass 50 kg climbs stairs by spending
1200 J of energy. How high does the boy climb
up? [Take g = 10 ms 2]
[2.4 m]​

Answer 1

4. Energy stored is potential energy

   Weight=W= 2(10)= 20 N

   U= mgh =  W*h = 2*10*60 = 1200 J

5. At highest point energy will be converted to potential energy

   W= 0.25*10 = 2.5 N

   U=Wh = 2.5*40 = 100J

6. Energy spent = Potential energy at max height

   1200 = mgh = 50*10*h

   or h= 2.4 m

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Answer 2

weight :- 2 kgf = 2 x 10 = 20

height = 60m

potential energy = force into height

= 20 x 60

= 1200J