Mechanical Engineering Principles

152 MECHANICAL ENGINEERING PRINCIPLES Which of the following statements is false? (a) An externally applied force is needed to ...

14 Work, energy and power At the end of this chapter you should be able to: define work and state its unit perform simple calcu ...

154 MECHANICAL ENGINEERING PRINCIPLES 500 Force / N 020 Extension / mm Figure 14.2 =^12 ×( 20 × 10 −^3 )m×500 N =5J It is shown ...

WORK, ENERGY AND POWER 155 1000 500 0 5 10 15 Distance / m Force / N 20 AB CD E F G Figure 14.4 pointsCandDa constant force of 5 ...

156 MECHANICAL ENGINEERING PRINCIPLES work done=^12 ×base×height =^12 × 30 × 10 −^3 m×6N = 90 × 10 −^3 J= 0 .09 J (b) Work done ...

WORK, ENERGY AND POWER 157 =5820 kN mm=5820 N m =5820 J Hence the work done as the tool moves through 100 mm is5.82 kJ Now try t ...

158 MECHANICAL ENGINEERING PRINCIPLES (xii) Sound energy is converted to electrical energy by a microphone. (xiii) Electrical en ...

WORK, ENERGY AND POWER 159 For the gearing, efficiency = output energy input energy i.e. 75 100 = 10000 input energy from which, ...

160 MECHANICAL ENGINEERING PRINCIPLES Power= work done time taken = 39 240 J 20 s =1962 W or 1 .962 kW Problem 15. 10 kJ of work ...

WORK, ENERGY AND POWER 161 (b) Power output =force×velocity, from which, velocity= power output force . Force acting on the 300 ...

162 MECHANICAL ENGINEERING PRINCIPLES A car towing another at 54 km/h exerts a steady pull of 800 N. Determine (a) the work don ...

WORK, ENERGY AND POWER 163 If friction is present, then work is done overcoming the resistance due to friction and this is dissi ...

164 MECHANICAL ENGINEERING PRINCIPLES (a) Initial kinetic energy=^12 mv^2 =^12 ( 4 )( 400 )^2 =320 kJ (b) At a height of 1 km, p ...

WORK, ENERGY AND POWER 165 Determine the braking power required to give this change of speed. Change in kinetic energy of car =^ ...

166 MECHANICAL ENGINEERING PRINCIPLES But ∑ mr^2 =I Therefore, kinetic energy (in rotation)=^12 Iω^2 (J) whereI=the mass moment ...

WORK, ENERGY AND POWER 167 The kinetic energy of a body of massm kg and moving at a velocity ofvm/s is given by...... State the ...

168 MECHANICAL ENGINEERING PRINCIPLES Neglecting air resistance, the initial kinetic energy possessed by the bullet is: (a) 6.48 ...

WORK, ENERGY AND POWER 169 Assignment 4 This assignment covers the material con- tained in chapters 11 to 14. The marks for each ...

15 Friction At the end of this chapter you should be able to: understand dynamic or sliding friction appreciate factors which a ...

FRICTION 171 Transposing gives: frictional force =μ×normal force, i.e. F=μN The direction of the forces given in this equation i ...