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A 900-N lawn roller is to be pulled over a 5-cm (high) curb. Radius of roller is 25 cm. What minimum pulling force is needed if angle made by handle is (a) 0 deg (b) 30 degrees?

Respuesta :

I believe b 30 degrees 

The minimum pulling force when the angle is 0 degrees = 0.675 kN

The minimum pulling force when the angle is 30 degrees = 0.54 kN

Given data :

Radius of roller = 25 cm

Height of curb = 5 cm

Force of Lawn roller = 900-N

First step : Determine angle made by the reaction force with the vertical axis

cos ∝ = ( 25 - 5 ) / 5

          = 20 / 5 = 4

∴ ∝ = cos⁻¹ 4 = 36.87°

Step two : Determine the minimum pulling forces  

applying the horizontal force balance equation

∑Fₓ = 0

Fcos ∅ + R sin ∝ = 0 --- ( 1 )

where R ( vertical force balance equation ) = ( W - Fsin∅ ) / cos ∝

Back to equation ( 1 )

The horizontal force balance equation Fₓ becomes

F = ( W sin ∝ ) / cos ( ∅ - ∝ )

Final step :

A ) When the angle ( ∅ ) = 0 degrees

F = ( 900 * sin 36.87 )  / cos ( 0 - 36.87

  = 675 N = 0.675 kN

B) When the angle (  ∅ ) = 30 degrees

F = ( 900 * sin 36.87 ) / ( cos ( 30 - 36.87 )

  = 540 N = 0.540 kN

Hence we can conclude that the minimum pulling force when the angle is 0 degrees = 0.675 kN and The minimum pulling force when the angle is 30 degrees = 0.54 kN

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