## korosh23 one year ago Physics questions!

1. korosh23

2. korosh23

Please answer the orange questions which there is a question mark. Each question in a different page. So three medals.

3. korosh23

Ok #36 please! I have my answer. I will send it in a sec!

4. korosh23

5. Michele_Laino

I got this: |dw:1433908300305:dw| so I can write this: $\Large {m_1}{v_1} - {m_2}{v_2} = \left( {{m_1} + {m_2}} \right)v$ from which I got: v= +4 m/sec

6. korosh23

How !?

7. Michele_Laino

using my reference system, we can write: $\Large \begin{gathered} {{\mathbf{v}}_{\mathbf{1}}} = \left( {{v_1},0} \right) \hfill \\ {{\mathbf{v}}_{\mathbf{2}}} = \left( { - {v_2},0} \right) \hfill \\ \end{gathered}$

8. korosh23

Are you sure that is m1v1 - m2v2 or m1v1 + m2v2?

9. Michele_Laino

no, since what is conserved is the vector which represents the total momentum, actually our equation is: $\Large {m_1}{{\mathbf{v}}_{\mathbf{1}}} + {m_2}{{\mathbf{v}}_{\mathbf{2}}} = \left( {{m_1} + {m_2}} \right){\mathbf{v}}$

10. korosh23

Exactly, it is a closed system. Energy is conserved. Now lets plug in the numbers.

11. Michele_Laino

now we have to go from vectors to components, and as I wrote before, we can write: $\begin{gathered} {{\mathbf{v}}_{\mathbf{1}}} = \left( {{v_1},0} \right) \hfill \\ {{\mathbf{v}}_{\mathbf{2}}} = \left( { - {v_2},0} \right) \hfill \\ \end{gathered}$

12. korosh23

what is v2? Motor or truck?

13. Michele_Laino

v_2 is the motor

14. Michele_Laino

furthermore: $\Large {v_1} = \left| {{{\mathbf{v}}_{\mathbf{1}}}} \right|,\quad {v_2} = \left| {{{\mathbf{v}}_{\mathbf{2}}}} \right|$

15. korosh23

Wait a moment.

16. korosh23

In the question it says the truck is going west. West is the negative direction. Motorist is going opposite of west which is east! It is postive velocity. Truck should have -ve velocity.

17. Michele_Laino

ok! Then our correct drawing is: |dw:1433908946956:dw| and the previous equation will become: $\Large \begin{gathered} - {m_1}{v_1} + {m_2}{v_2} = \left( {{m_1} + {m_2}} \right)v \hfill \\ {{\mathbf{v}}_{\mathbf{1}}} = \left( { - {v_1},0} \right) \hfill \\ {{\mathbf{v}}_{\mathbf{2}}} = \left( { + {v_2},0} \right) \hfill \\ \end{gathered}$

18. Michele_Laino

and the answer is: v= -4 m/sec

19. korosh23

That means I was right? I got -4 m/s

20. Michele_Laino

yes!

21. korosh23

Ok great, thank you! I have to go, I will ask my other questions later.

22. Michele_Laino

ok!

23. korosh23

Just wondering are you here in openstudy tomorrow. On Thursday I have a physics exam. I was wondering if I have few quick question, Is it ok I ask you?

24. Michele_Laino

yes! I will stay in OpenStudy tomorrow, and I can help you

25. korosh23

At what time are you in openstudy, and when you leave?

26. Michele_Laino

I will be here in OpenStudy at 6:00 am (Italy Time zone)

27. korosh23

Ok I will manage mt time. Thank you, you are a very supportive tutor.

28. Michele_Laino

:)