Physics 407 Exam #3

Closed book.  Do all questions.
Part I.  Do all 8 questions. 5 pts each

1.)   can be expressed in

1. kg m
2. kg m/s
3. kg m/s²
4. kg m²/s²                              

2.) A truck at rest at the top of the hill rolls down and achieves a speed of 12 m/s at the bottom. In a second experiment, the same truck has an intial speed of 5 m/s at the top of the hill. Its speed v_f at the bottom will be:

1. 7 m/s
2. 8 m/s
3. 13 m/s
4. 17 m/s                               

3.)  It takes 10 Nm of work to compress an ideal spring 12 cm.  How much work does it take to compress it 24 cm?

1. 14 Nm
2. 20 Nm
3. 34 Nm
4. 40 Nm                                          

4.)  A 2.0 kg particle with total energy of 6 J is trapped in the potential "well" below.  When the particle is at  x = 3.5 m, its acceleration is: [hint: calculate the force and use Newton's 2^nd law]

1. 1 m/s²
2. -1 m/s² 
3. +3 m/s²
4. - 3 m/s²                             

5.) When the m = 2kg block slides down the plane, it reaches a final speed at the bottom of v_F = 7.0 m/s. The initial potential energy dissipated as heat is:

1. 0 
2. 7.0 J
3. 15 J
4. 49 J                                  

6.)  A tennis racket strikes a tennis ball with a force  F = F(t) whose graph is shown below:

The total linear momentum change Æp given to the tennis ball is:

1. 0
2. 5 kg m/s
3. 10 kg m/s
4. 20 kg m/s

7.) The center of mass of the two particles below is at x _cm =

1. 0 m
2. 0.8 m
3. 1.2 m 
4. 1.6 m

8.)  Two identical hockey pucks collide on horizontal, frictionless ice.                                      

What must be the final speed v_f of the top puck?

1. 0.45 m/s
2. 1.155 m/s
3. 0.1155 m/s
4. 0
5. I need v_o to answer this question

Part II.  Do both problems.  30 pts each.  Write complete equations.  SHOW ALL YOUR WORK.

1.) A small roller coaster of mass m has an initial horizontal speed of 4.0 m/s at point A at the top of the hills.  It rolls down over the smaller hill and coasts horizontally a distance L and comes to a stop. Calculate: [You must start with a physical law and then proceed logically, step-by-step, to obtain full credit.  Don't forget units in your answer.]

1. the roller coaster's speed at point C (10)
2. how far it rolls (L) on the horizontal surface which has a coefficient of kinetic friction of m = 0.2.  (20)

2.)  A bullet of mass m₁ and horizontal speed v_o strikes a stationary block of mass m₂. Calculate (in symbols):  [You must start with a physical law, write complete equations and include every step in your answer to get full credit.]        

1. the final speed of the bullet and block in terms of  m₁, m₂, and v_o. (10)
2. the ratio of   in terms of m₁ and m₂ (10)
3. Which kinetic energy is larger KE intial or KE final? Where did the difference in kenitic energy go? (10)

KE initial = total KE of system of m₁ + m₂ before bullet strikes m₂

KE final = total KE of system of m₁ + m₂ after bullet comes to rest in m_2.