Velocity as a function of time

Please explain how to interpret this graph as well as the rest of the problem. Thank you!

Two horizontal forces http://edugen.wiley.com/edugen/cours...ta/up/Fvec.gif1 and http://edugen.wiley.com/edugen/cours...ta/up/Fvec.gif2 act on a 3.0 kg disk that slides over frictionless ice, on which an *xy* coordinate system is laid out. Force http://edugen.wiley.com/edugen/cours...ta/up/Fvec.gif1 is in the positive direction of the *x* axis and has a magnitude of 6.7 N. Force http://edugen.wiley.com/edugen/cours...ta/up/Fvec.gif2 has a magnitude of 9.0 N. Figure 5-34 gives the *x* component *vx* of the velocity of the disk as a function of time *t* during the sliding. What is the angle between the constant directions of forces http://edugen.wiley.com/edugen/cours...ta/up/Fvec.gif1 and http://edugen.wiley.com/edugen/cours...ta/up/Fvec.gif2?

http://edugen.wiley.com/edugen/cours...5/fig05_34.gif**Fig. 5-34**

*Problem 12.*