## Py 120 Test 2 Spring 1998

Name: _____________________ Pledged:___________________________

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**### Part A: Interactive Problem. (20 pts)

**
**
- The animation shows a perfectly elastic ball dropped from a height h and bouncing off of
the floor. Sketch the potential energy (PE), kinetic energy (KE), and total energy (E) as
functions of time for the animation shown on the computer monitor. Do all plots on the
same graph. That is, use one set of axes and draw all three functions. Clearly label the
functions and show the times when the ball hits the ground. Make sure your sketch shows
three bounces.
** Begin **

**
**### Part B: Concept problems. (20 pts each.) These are short but you must still GIVE YOUR
REASONS.

**
**
- Two satellites, A and B, of the same mass are going around the earth in concentric
orbits. Satellites B is going around the Earth at twice the distance from the Earth's
center as satellite A. What is the ratio of the centripetal force acting on satellite B to
that acting on satellite A?
- A spring loaded dart gun is used to shoot a dart straight up into the air. The dart
reaches a maximum height of 24 m. The same dart is shot straight up a second time but the
spring is compressed only half as far before firing. How far up does the dart go this
time? Ignore friction.

**Part C: Textbook problem (40 pts total.)**

- Two objects of equal mass collide head on. The velocity of object 1 is 3 m/s heading
east and that of object two is 4 m/s heading west.

a) (10 pts.) What is the speed of each object after the collision if they stick together?

b) (10 pts.) What is the speed of each object after the collision if the collision is
perfectly elastic?

c) (5 pts.) Was any mechanical energy lost in either (a) or (b)? If so, how much?

- (15 pts) A child ties a 400 gr rock to 50 cm of 6 lb fishing line. That is, the line
will break when the tension exceeds 6 lb. She starts to swing the rock in a vertical
circle (e.g., like a Ferris wheel) until the string breaks. Where is the rock when the
line breaks and what is the speed of the rock when the line breaks.

( 1 lb = 4.45 N, g = 9.8 m/s^{2})