Clayton State University
Department of Natural Sciences
November 1, 2013
Physics 2211 – Quiz 9
Name __SOLUTION __________________________________
Two cars of masses m1 (1300 kg) and m2 (2000 kg) collide at an intersection. Before the
collision, car 1 was traveling eastward at a speed of v1 (15.0 m/s), and car 2 was traveling
northward at a speed of v2 (20.0 m/s). After the collision, the two cars stick together and
travel off in the direction shown.
a. Find the speed v of the two-car unit after the collision.
Before collision:
ptot, x  m1V1ix  m2V2ix  (1300 kg)(15.0 m / s)  19500 kgm / s
ptot, y  m1V1iy  m2V2iy  (2000 kg)(20.0 m / s)  40000 kgm / s
After collision:
ptot, x  (m1  m2 )V fx  (3300 kg)V fx  19500 kgm / s
V fx  5.91 m / s
ptot, y  (m1  m2 )V fy  (3300 kg)V fy  40000 kgm / s
V fy  12.1 m / s
Vf=13.5 m/s
b. Find the angle θ.
  tan 1 (V fy / V fx )  64.0 o
c. Suppose that after the collision, tanθ=1; in other words, θ is 45∘. This means
that before the collision:
i.
The magnitudes of the momenta of the cars were equal.
ii.
The masses of the cars were equal.
iii.
The velocities of the cars were equal.