student_lfcs Posted August 8, 2019 Share Posted August 8, 2019 Ques: An 8000 kg engine pulls the train of 5 wagons, each of 2000 kg, along a horizontal track. If the engine exerts a force of 40000 newton and the track offers a frictional force of 5000 newtons then calculate the force of wagon 1 on wagon 2. Ans ( I tried) : Total weight =18,000 kg Net force exerted= 40000 - 5000 = 35000 Accelration: 35000 / 18000 = 35 / 18 = 3.5 m/s^2 Link to comment Share on other sites More sharing options...
studiot Posted August 8, 2019 Share Posted August 8, 2019 Quote Ans ( I tried) : Total weight =18,000 kg kg are a measure of mass not weight. 12 minutes ago, student_lfcs said: Net force exerted= 40000 - 5000 = 35000 Is the net force the same between all parts of the train? Link to comment Share on other sites More sharing options...
student_lfcs Posted August 13, 2019 Author Share Posted August 13, 2019 Ok. Please see if I am right this time: Total mass =18,000 kg Net force exerted= 40000 - 5000 = 35000 Accelration: 35000 / 18000 = 35 / 18 = 1.95 m/s^2 force exerted by wagon 1 on wagon 2: Accelration x Mass Mass in this case = 4 x 2000 = 8000 kg; Accelration is same i.e. 1.95 m/s^2 So F = 8000 x 1.95 = 15555 N Link to comment Share on other sites More sharing options...
studiot Posted August 13, 2019 Share Posted August 13, 2019 (edited) 1 hour ago, student_lfcs said: Ok. Please see if I am right this time: Total mass =18,000 kg Net force exerted= 40000 - 5000 = 35000 Accelration: 35000 / 18000 = 35 / 18 = 1.95 m/s^2 force exerted by wagon 1 on wagon 2: Accelration x Mass Mass in this case = 4 x 2000 = 8000 kg; Accelration is same i.e. 1.95 m/s^2 So F = 8000 x 1.95 = 15555 N OK that looks a whole lot better. Hopefully you feel good too since I didn't do it for you, just offered a hint. One small niggle. My calculator says that 35/18 = 1.94 not 1.95. In fact there is no need to work this out at all. Just leave the common acceleration* as [math]\left( {\frac{{35}}{{18}}} \right)[/math] Then you can multiply it all out at the end. Very often something will cancel out and make it even easier. [math]F = ma = 8000*\left( {\frac{{35}}{{18}}} \right)[/math] * Notice also how to spell acceleration. Edited August 13, 2019 by studiot Link to comment Share on other sites More sharing options...
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