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Homework Help: Questions regarding HEAT & ENERGY

  1. Oct 17, 2005 #1
    1. Consider a perfectly inelastic collision of two objects of equal mass.

    A. Is the loss of kinetic energy greater if the 2 objects have oppositely directed velocities of equal magnitude, v/2, or if one of the two objects is initially at rest and the other has an initial velocity of v?

    B. In which situation is the percentage loss in kinetic energy the greatest?

    2. Answer true or false for each:

    A. In any perfectly inelastic collision, all the kinetic energy of the bodies is lost.

    B. In a head-on elastic collision, the relative speed of recession after the collision equals the relative speed of approach before the collision.

    C. Mechanical energy is conserved in an elastic collision.

    3. You kick a soccer ball of mass 0.43 kg. The ball leaves your foot with an initial speed of 25 m/s.

    A. What is the impulse imparted to the ball by you?

    B. If you foot is in contact with the ball for 0.008 s, what is the average force exerted by your foot on the ball?

    5. A 16 g bullet is fired into the bob of a ballistic pendulum of mass 1.5 kg. When the bob is at its maximum height, the string makes an angle of 60o with the vertical. The length of the pendulum is 2.3 m. Find the speed of the bullet.

    6. A 2000 kg car, traveling to the right at 30 m/s, is chasing a second car of the same mass that is traveling to the right at 10 m/s.

    A. If the 2 cars collide and stick together, what is their speed just after the collision?

    B. What fraction of the initial kinetic energy of the cars is lost during this collision? Where does it go?

    7. A 3 kg block is traveling to the right at 5 m/s and a second 3 kg block is traveling to the left at 2 m/s. What is the total kinetic energy of the system?

    8. A 5 kg object with a speed of 4.0 m/s collides head-on with a 10 kg object moving toward it with a speed of 3.0 m/s. The 10 kg object stops dead after the collision.

    A. What is the final speed of the 5 kg object?

    B. Is the collision elastic?

    9. A suspicious package is sliding on a frictionless surface when it explodes into 3 pieces of equal mass and with the velocities of

    1- 7.0 m/s, north

    2- 4.0 m/s, 30o south of west

    3- 4.0 m/s, 30o south of east

    A. What is the velocity (magnitude and direction) of the package before it explodes?

    B. What is the displacement of each piece (with respect to their positions together before the explosion) 3.0 s after the explosion?

    10. A 3.0 kg object moving at 8.0 m/s in the positive direction of x has a one-dimensional, completely elastic collision with another object of mass M, initially at rest. After the collision the object of mass M has a velocity of 6.0 m/s in the positive direction of x. What is the mass M?

    11. A movie set machine gun fires 50 g bullets, each at a speed of 100 m/s. An actor, holding the machine gun in his hands, can exert an average horizontal force of magnitude 180 N against the gun. Determine the maximum number of bullets he can fire per minutes while still holding the gun steady.

    12. A 5.0 kg ball moving due east at 4.0 m/s collides with a 4.0 kg ball moving due west at 3.0 m/s. Just after the collision, the 5.0 kg ball has a velocity of 1.2 m/s, due south.

    A. What is the magnitude of the velocity of the 4.0 kg ball just after the collision?

    B. By how much is the mechanical energy of the 2 ball system reduced by the collision?

    ANY help will do fine.. thanks in advance!
  2. jcsd
  3. Oct 17, 2005 #2


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