1 Answers
Option 1 : 8.1 cm
Given :
A cone was cut parallel to its base into 2 pieces
The ratio of the volume of the smaller cone formed and another part is 64: 61
The height of the cone = H = 40.5 cm
The height from the base at which the cut was made is to be calculated
Formula Used:
The volume of cone = πr2h/3
Concept Used:
If r and R are the radii of smaller cone and whole cone
And h and H are the radii of smaller cone and whole cone
Then r/R = h/H
Calculation:
Let the height from base at which cut was made be 'h'
Since, Cone was cut parallel to its base into 2 pieces
Height of upper cone = H – h = (40.5 – h) cm
The volume of upper cone = 1/3 × π × r² × (40.5 - h)
The volume of whole cone = 1/3 × π × R² × 40.5
Now, Ratio of volume = 1/3 × π × r² × (40.5 - h) : 1/3 × π × R² × 40.5
⇒ r² × (40.5 - h) : R² × 40.5 = 64 : (64 + 61)
⇒ r² × (40.5 - h) : R² × 40.5 = 64 : 125
Now, according to the concept used, r/R = (40.5 - h)/40.5
⇒ (40.5 - h)3 : 40.53 = 64 : 125
⇒ (40.5 - h) : 40.5 = 4 : 5
⇒ (40.5 - h) = 32.5
⇒ h = 8.1
∴ Height from the base where cut is made = 8.1 cm