Mechanical Engineering Principles

126 MECHANICAL ENGINEERING PRINCIPLES

Assignment 3

This assignment covers the material

contained in Chapters 8 to 10.

The marks for each question are shown

in brackets at the end of each question.

1. A beam, simply supported at its ends, is
   of length 1.4 m. If the beam carries a
   centrally-placed downward concentrated
   load of 50 kN, determine the minimum
   permissible diameter of the beam’s cross-
   section, given that the maximum permis-
   sible stress is 40 MPa, and the beam has
   a solid circular cross-section.
   (6)


2. Determine the force applied tangentially
   to a bar of a screw-jack at a radius of
   60 cm, if the torque required is 750 N m.
   (3)


3. Calculate the torque developed by a
   motor whose spindle is rotating at 900

rev/min and developing a power of

4.20 KW. (5)

4. A motor connected to a shaft develops a
   torque of 8 kN m. Determine the number
   of revolutions made by the shaft if the
   work done is 7.2 MJ. (6)


5. Determine the angular acceleration of a
   shaft that has a moment of inertia of
   32 kg m^2 produced by an accelerating
   torque of 600 N m. (5)


6. An electric motor has an efficiency of
   72% when running at 1400 rev/min.
   Determine the output torque when the
   power input is 2.50 kW. (5)


7. A solid circular section shaft is required to
   transmit 60 hp at 1000 rpm. If the maxi-
   mum permissible shear stress in the shaft
   is 35 MPa, determine the minimum per-
   missible diameter of the shaft. What is
   the resulting angle of twist of the shaft per
   metre, assuming that the modulus of rigid-
   ityG=70 GPa and 1 hp= 745 .7W?
   (10)