Physics Review Chapters 6, 7

Objectives/vocabulary:

  1. Know the definition of centripetal force, and what causes it.
  2. Be able to calculate centripetal force and acceleration.
  3. Solve problems involving universal gravitation.
  4. Define momentum and impulse and use the impulse-momentum theorem
  5. Use law of conservation of momentum to solve problems.
  6. Understand the difference between elastic and inelastic collisions.

Multiple choice practice:

  1. How would an angle in radians be converted to an angle in degrees?
  2. The angle in radians would be multiplied by 180o/.
  3. The angle in radians would be multiplied by 360 o /.
  4. The angle in radians would be multiplied by 180 o/2.
  5. The angle in radians would be multiplied by 2/360 o.
  1. A cave dweller rotates a pebble in a sling with a radius of 0.30 m counterclockwise through an arc length of 0.96 m. What is the angular displacement of the pebble?
  2. 1.6 rad
  3. –1.6 rad
  4. 3.2 rad
  5. –3.2 rad
  1. A bucket on the circumference of a water wheel travels an arc length of 18 m. If the radius of the wheel is 4.1 m, what is the angular displacement of the bucket?
  2. 1.0 rad
  3. 4.4 rad
  4. 3.7 rad
  5. 2.3 rad
  1. A grinding wheel initially at rest with a radius of 0.15 m rotates until it reaches an angular speed of 12.0 rad/s in 4.0 s. What is the wheel's average angular acceleration?
  2. 96 rad/s2
  3. 48 rad/s2
  4. 3.0 rad/s2
  5. 0.33 rad/s2
  1. A potter's wheel moves from rest to an angular speed of 0.54 rad/s in 30.0 s. What is the angular acceleration of the wheel?
  2. 16 rad/s2
  3. 1.3 rad/s2
  4. 0.018 rad/s2
  5. 0.042 rad/s2
  1. A bicycle wheel rotates with a constant angular acceleration of 3.0 rad/s2. If the initial angular speed of the wheel is 1.5 rad/s, what is the angular displacement of the wheel after 4.0 s?

  1. 6.0 rad
  2. 24 rad
  3. 3 x 101 rad
  4. 36 rad

  1. A ball rolls downhill with an angular speed of 2.5 rad/s and has a constant angular acceleration of 2.0 rad/s2. If the ball takes 11.5 s to reach the bottom of the hill, what is the final angular speed of the ball?
  2. 13 rad
  3. 31 rad/s
  4. 33 rad/s
  5. 25.5 rad/s
  1. The end of the cord on a weed cutter is 0.15 m in length. If the motor rotates at the rate of 126 rad/s, what is the tangential speed of the cord?
  2. 628 m/s
  3. 25 m/s
  4. 19 m/s
  5. 63 m/s
  1. A cylinder with a diameter of 0.150 m rotates in a lathe at a constant angular speed of 35.6 rad/s. What is the tangential speed of the surface of the cylinder?
  2. 2.67 m/s
  3. 5.34 m/s
  4. 2.37 x 102 m/s
  5. 4.75 x 102 m/s
  1. A point on the rim of a rotating wheel with a 0.37 m radius has a centripetal acceleration of 19.0 m/s2. What is the angular speed of the wheel?
  2. 0.89 m/s
  3. 1.6 rad/s
  4. 3.2 rad/s
  5. 7.2 rad/s
  1. A 0.40 kg ball on a 0.50 m string rotates in a circular path in a vertical plane. If the angular speed of the ball at the bottom of the circle is 8.0 rad/s, what is the force that maintains circular motion?
  2. 5.6 N
  3. 11 N
  4. 13 N
  5. 20.0 N
  1. The total amount of momentum in a closed, isolated system
  2. is constantly increasing
  3. is constantly decreasing
  4. is conserved
  5. is radical
  1. A change in the kinetic energy during a collision means that ____ .
  2. the collision is inelastic
  3. the collision is elastic
  4. conservation of momentum is not true
  5. none of these
  1. When a net force not equal to zero acts on a body ____ .
  2. the velocity of the body is constant
  3. the body is accelerating
  4. the momentum of the body is zero
  5. the momentum is increasing
  1. The smallest change in momentum will be produced by ____ .
  2. a large force over a short time
  3. a small force over a short time
  4. a small force over a long time
  5. a large force over a long time
  1. If an object with a velocity of 40 m/s has the same momentum as that of a 10 kg mass having a velocity of 20 m/s, the mass of the object is ____ .
  2. 10 kg
  3. 8 kg
  4. 5 kg
  5. 1 kg
  1. Impulse can be represented by ____ .
  2. change in velocity divided by time
  3. force times time force is applied
  4. mass times velocity
  5. none of the above
  1. When a bat hits a baseball, the force exerted by the bat on the ball is ____ that exerted by the ball on the bat.
  2. equal to
  3. greater than
  4. less than
  1. When a bat hits a baseball, the change in momentum of the ball is _____ that of the bat.
  2. equal to
  3. greater than
  4. less than
  1. When a bat hits a baseball, the change in velocity of the ball is ____ that of the bat.
  2. equal to
  3. greater than
  4. less than

Problems

1. How does the gravitational force of a 550 kg object -20.0 m above the ground, compare with that of a 350 kg object 30.0 m above the ground?

2. A car with a mass of 1500 kg hits a parked 18 wheeler with a mass of 4000 kg and sticks to it.

The two cars continue traveling at 2.0 m/s. How fast was the car moving at the moment of impact?

= 7.3 m/s

3. The 2.0 kg head of an axe is moving at a velocity of 5.0 m/s when it strikes a log and penetrates 0.02 m into the log.

a. What was the impulse imparted on the axe?

b. How muchforce is exerted on the log?

c. What is the average acceleration of the blade?

4. What amount of acceleration of a 30 kg cart that is pushed 4.0 m across the floor bya horizontal 50 N force?

5. What was the change in momentum of the cart in #4?

6. What is the acceleration due to gravity on Pluto? (mpluto = 5 x 1023 kg, rpluto = 4 x 105 m)

g = 208.53 m/s2

7. Earth has a mass of about 5.98 x 1024 kg, and our Moon has a mass of about 7.36 x 1022 kg. If the magnitude of the gravitational force between the two bodies is 1.99 x 1020 N, how far apart are the Earth and the Moon?

r = 3.84 x 108 m

Use this information to answer the questions following:

An airplane is flying in a horizontal circle and experiences 5 g’s at a speed of 105 m/s. The pilots mass is 80.0 kg pilot. (g = 9.81 m/s2)

8. What is the radius of the turn?

225 m

9.At this radius, what is the magnitude of the net force that maintains circular motion exerted on the pilot

Fc = 3920 N