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Principles of Engineering Mechanics (2nd Edition) Episode 3

Tham khảo tài liệu 'principles of engineering mechanics (2nd edition) episode 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 36 Kinetics of a particle in plane motion .__ Time s Figure 3.32 3.18 In the test rig for an ejector seat Fig. 3.33 a the seat containing a dummy has a total mass of 500 kg. It is propelled up the launching guide by a rocket which develops a thrust whose magnitude T varies as shown by the graph in Fig. 3.33 b . Time s Figure 3.33 a Find the maximum acceleration to which the dummy is subjected. b Estimate the velocity of the dummy 1.2 s after the rocket is fired. Air resistance and friction in the guides may be neglected. The mass of the fuel burned is small and may also be neglected. 3.19 A small jet aircraft has a mass of 7350 kg and a jet thrust of 50 kN. During take-off resistance to motion is equal to the sum of the aerodynamic drag force and the rolling resistance of the wheels the latter force is equal to 0.02 times the normal reaction. Lift forces also act on the aircraft and both the lift and drag vary with the horizontal velocity of the aircraft in the manner shown in Fig. 3.34. Estimate the minimum length of runway required for take-off. Assume that the jet thrust and drag are always horizontal and that the lift forces act only vertically during take-off. The entire aircraft can be considered to be a rigid body in translation with wheels of negligible mass. Figure 3.35 3.20 See Fig. 3.35. A lunar module p of mass 15000 kg is approaching the Moon which has a surface gravity of 1.62 N kg and a mean radius of 1738 km. The centre of the Moon is taken as an origin o. When the module is 80 km from the surface its velocity V is inclined at 45 from the line OP. The reverse thrust T of the descent engine then has a magnitude of 44.5 kN and is inclined at 15 to the line OP. Determine a the magnitude of the component of the acceleration of the module along the radial line OP and b the magnitude of the component of the acceleration of the module normal to its flight path. Velocity M s Figure 3.34 4 Force systems and equilibrium 4.1 Addition of forces Force has .