Question

A 25000 Kg airplane takes off from rest and reaches 5000m altitude and cruises at 900km/h in 8 minutes .Find Avg Power ?

Answer 1

My Work:

Pavg = W/t

W = Delta K.E

W = 25000 * 250*250 / 2

t = 8 * 60

Answer 2

i got Pavg = 1.6 MW but the answer shuld be 4.2 MW

Answer 3

Hang on a bit...

Answer 4

You have forgotten the gain in gravitational potential energy.

Answer 5

We have Consider P.E here ?

Answer 6

Of course! How could you raise the altitude of the plane without providing energy?!

Answer 7

Yup...i got..it...thx..)

Answer 8

but @Vincent-Lyon.Fr we knw change in K.E is Work Done..Why cant we Use it here..)

Answer 9

Is it then mgh+delta K.E /t ?

Answer 10

You can, but there are two works to take into account:
- motive work by the engine (positive)
- negative work by the weight

so change in KE = Wengine - Mgh
or
W engine = change in KE + change in PE

Answer 11

Ok...Thxx....

Answer 12

yw :)

Answer 13

I see you are now getting to the energy concept. Soon you will be able to solve problems of mechanics by this method.