Question

A right triangle whose sides are 15cm and 20cm is made to revolve about it's hypotenuse. Find the volume and the surface area of the double cone so formed

Answer 1

Answer:

V=3771 cc

A=2639 sq cm

Step-by-step explanation:

Third side=25cm

And we rotate the tri.' around this hypotenuse. So we have 2 cones glued base to base.

Their radii will be same.

r/20=sin a=0.6 where a is slant angle of cone face with axis.

So r=12 for common base of both cones.

1) For big cone:

A=2πr(hs) where hs is slant height

A=2π*12*20=1508

and

V=π*r*r*h/3

=π*12*12*(20*cos a)/3

=144π*(20*cos 36.87)/3

=144π*(20*0.8)/3

=2413

2) For small cone:

A=2π*12*15=1131

and

V=π*12*12*9/3=1358

Total area

=1508+1131=2639

and

Total vol.

=2413+1358

=3771