Some physics problems (3)

Problem:

Jack has got an engine failure and is calling Janice to get towing assistance. Janice unable to come because he is in the middle of dinner. Instead, Atle comes. It is completely flat from where the car to Per stands and home to the courtyard. Below is a figure showing the towing.

a) Calculate the acceleration of a wagon train. Assume zero friction and air resistance.

b) What will the string power K become?



Solution:

By applying Newton's second law to the whole object,we have

$ \begin{eqnarray*} F &=& ma \\ 2000 &=& (1900+1100)a \\ a &=& \frac{2}{3} kgms^{-2} \\ \end{eqnarray*} $

Part b)

There is no such thing called string power. I guess the problem is asking for the tension developed on the string.

Once again, we apply the Newton's second law, but this time to $ m_2 $.


$ \begin{eqnarray*} F &=& ma \\ K &=& (1100)\frac{2}{3} \\ &=& \frac{2200}{3} N \\ \end{eqnarray*} $

By Newton's third law, the same tension is applied from the string to both cars.