There was a circular meadow with diameter 160 m. A labourer wanted to mow the grass of the meadow with a mower of width 20 m and working with a speed of 113.3 km/hr. In how many seconds did he finish mowing the meadow ?
Please let me know how to proceed in the question
My attempt:-
Let the length of the mower be x meters, therefore are of the cross section of mower would be 20*x
Since the complete meadow has to be mowed,
Area of field = Total area mowed by the mower
Let t be the time required in seconds by the mower to do the task
$π * (80)^2 = t * (20*x*113.3*\frac{1000}{60*60})$
I have 2 variables in here , how to eliminate one of them ?
I think you misinterpreted the problem.
The width of the blade is actually the oher side of the blade.
The lenght is irrelevant,because only the edge of the blade is cutting the grass.
The speed of the mower is $113.3km/h$,so it cuts $113.3km/h*20m$ in one hour. So: $$\pi*(80m)^2=t*113.3km/h*20m$$ $$t=\pi*6400m^2÷113300m*3600s÷20m$$ $$t=32s$$ This is the only way I see of solving this.
There is also a mistake in your attempt,which we can use to prove my theory.
When you wrote $$π∗(80)^2=t∗(20∗x∗113.3∗\frac{1000}{3600})$$ you didn't use the measurement quantities.Let's insert them now. $$π∗(80m)^2=t∗(20m∗xm∗113.3m∗\frac{1000}{3600})$$ When you solve this equation,you get $$t=32s÷xm$$ We all know time is not expressed in meters,so it's obvious there's one number too much and I think it's this $xm$.
I might be wrong,but I think that really just the edge side of the blade is relevant here.