Question

7. A crane can lift up 20,000kg of coal in 2 hours from a mine of 100m depth. If the efficiency of the crane is 90% its input power must be​

Answer 1

Use this method for your answer

plz don't write this answer

use this method

Let input power =P

Since 80 % of this power is being used, so effective power is 

10080P

Mass of coal m=10,000 kg

Time t=1×60×60 s

Height h=180 m

Gravitational acceleration g=10 m/s2 (given)

Now, Power = work / time

So, 10080P=60×6010,000×9.8×180

Simplifying we get: P=6.25 kW