Question

a block of ice falls from a hight and completely melts.if only 1/4 of the energy is retained by the block the height of the fall in km should be (g=10ms-2)?
​

Answer 1

Thus the height of the fall in L/ 2500 km

Explanation:

Potential energy of block = Thermal energy of ice block

1/4 mgh = mL

1/4 gh = L

h = 4 L / g

H = 4L / 10

h = 2 L/ 5 m x 1 Km / 1000 m

Thus the height of the fall in L/ 2500 km

Answer 2

The height of the fall is 0.15 km.

Explanation:

The potential energy of the block is equal to the thermal energy given out by the ice.

Potential energy of the block = Thermal energy of the ice block

1/4 × Potential energy of the block = Thermal energy of the ice block

Now, on substituting the formula for potential and thermal energy, we get,

1/4 × (mgh) = mL

1/4 × (gh) = L

h = 4L/g

Where, L = Latent heat of ice = 363 J/kg

Now, the height is:

h = (4 × 363)/9.8

∴ h = 148.2 m = 0.15 km