Monday 12 August 2013
FRICTION TUTORIAL
1) A
body on a rough horizontal surface requires a force of 240 N inclined at 250
just to pull it and 280 N just to push it at the same angle. Determine
the weight of the body and the coefficient of friction.
2) A
force of 2.4 KN parallel to the plane surface is required to just move a body
up an inclined plane, the angle of inclination being 80, when the
angle of inclination is increased to 120, the force required
increased to 3 KN. Determine the weight of the body and coefficient of
friction.
3) The
thrust on the propeller shaft of a marine engine is taken up by 8 collars whose
external and internal diameters are 660 mm and 420 mm respectively. The thrust
pressure is 0.4 MN/m2 and may be assumed uniform. The coefficient of
friction between the shaft and collar is 0.04. If the shaft rotates at 90 rpm
find 1) Total thrust on collar 2) power absorbed by friction at bearing.
4) Intensity
of pressure on a thrust bearing is not to exceed 40 × 104 N/m2.
The external and internal diameter of the collar is 200 mm and 150 mm
respectively. What should be the minimum number of collars for a total axial
thrust of 40 KN on the bearing? If the shaft rotates at 600 rpm and the
coefficient of friction is 0.08, determine the frictional power lost for uniform
pressure.
5) A
shaft has a number of collars integral with it. External diameter of collars is
400 mm and the shaft diameter is 250 mm. if the uniform intensity of pressure
is 35 × 104 N/m2, and its coefficient of friction is
0.05, estimate :
a.
Power absorbed in overcoming friction
when the shaft runs at 105 rpm and carries a load of 15 × 104 N.
b.
Number of collars required.
6) A
shaft carrying a load of 12 tonnes and running at 120 rpm has a number of
collars integral with it. Shaft diameter is 240 mm and the external diameter of
the collar is 360 mm. Intensity of uniform pressure is 400 KN/m2 and
the coefficient of friction is 0.06. Determine the power absorbed in overcoming
the friction and the number of collars required.
7) A
conical pivot bearing supports a vertical shaft of 300mm diameter. It is
subjected to a load of 30 KN. The angle of the cone is 1200 and the
co-efficient of friction is 0.03. Find the power lost in friction when speed is
100 rpm, assuming 1) uniform pressure and 2) uniform wear.
