Question

A flat plate of area 0.1 m2 is placed on a flat surface

and is separated from it by a film of oil

10-5 m thick whose coefficient of viscosity

1.5 N sm-2. The force required to cause the

plate to slide on the surface at constant speed

of 1 mm s-1 is

Answer 1

Given:

A flat plate of area 0.1 m2 is placed on a flat surface and is separated from it by a film of oil 10-5 m thick whose coefficient of viscosity 1.5 N sm-2.

To find:

The force required to cause the plate to slide on the surface at constant speed of 1 mm s-1 is

Solution:

From given, we have,

Area of flat plate = A = 0.1 m²

Thickness = dx = 10^{-5} m

Coefficient of viscosity = η = 1.5 Nsm^{-2} = 1.5 Pa

Velocity = dv = 1 mms^{-1} = 0.001 ms^{-1}

we use the formula,

F = ηA(dv/dx)

= (1.5 × 0.1 × 0.001) / (10^{-5}

= (1.5 × 10^{-4}) / (10^{-5}

∴ F = 15 N.