Some questions to help you prepare for the 2nd midterm exam PHYS101

Think carefully about the correct answer for each question and write it down. ONLY THEN are you allowed to click on the link for what you consider the correct answer to check yourself. If your answer disagrees from the correct one, this indicates that the concept involved may still be fuzzy to you. So make sure you study the corresponding lecture notes and chapters in the book carefully.

I. Which of the following statements about energy are correct? (More than one might be correct; write down all that are).

  1. Kinetic energy is always conserved
  2. Total mechanical energy is always conserved
  3. Work done by an external force can change both kinetic and potential energy
  4. The sum of all kinds of energy (including heat) within a closed system is always conserved.

II. A 5 kg mass lifted to a height of 10 m above the floor has a potential energy of roughly 500 J.

  1. Correct
  2. Wrong
  3. It depends what you chose for your reference height

III. If you fire a cannon straight up with double the muzzle speed,

  1. the cannonball will reach the same height.
  2. the cannonball will reach double the height.
  3. the cannonball will reach 4 times the height.
  4. the cannonball will reach 8 times the height.

IV. The angular velocity of Earth going around the sun is

  1. 2p/365/24/3600 rad/s
  2. approximately 2.10-7 rad/s
  3. 30 km/s
  4. roughly equal to g

V. What is the centripetal acceleration of a person standing on the surface of Earth?

  1. None, as long as they are standing still
  2. Much smaller than g
  3. Roughly equal to g
  4. Much larger than g

VI. If your toes and nose touch a wall and you try to stand on the tip of your toes, you will

  1. succeed if you are athletic enough
  2. fall over because there will be a net torque acting on you
  3. fall over because there will be a net force acting on you

VII. How much more torque do you need to set a long rod spinning at 1 round/sec around one of its ends compared to around its center? (check the formula sheet for appropriate information)

  1. Same torque
  2. 3 times as much
  3. 4 times as much
  4. That depends on how long you apply the torque

VIII. In the future, astronauts live in a huge rotating "wheel" to simulate the effects of gravity. Assume that they usually work in the "rim" of the wheel, but that the mess hall is in located in the "axle", so at lunchtime all astronauts walk along the spokes of the wheel to its center. What will happen? Check off ALL correct answers

  1. The wheel will slow its rotation a little bit
  2. The wheel will continue to rotate with exactly the same angular velocity
  3. The wheel's rotation will speed up
  4. The kinetic energy of the whole system (space station plus astronauts) is unchanged
  5. The astronauts have to do work to get to lunch
  6. Angular momentum is conserved

IX. A geostationary satellite circles Earth once every 24 hours. Moon takes about 27 days. How much further from the center of Earth than the satellite must Moon be?

  1. About 27 times
  2. Sqrt(27) which is approximately 5 times
  3. (27)^(3/2) which is approximately 140 times
  4. (27)^(2/3) which is approximately 9 times

X. A cannon fires a cannonball horizontally from a height H above ground. It strikes the ground a distance D away from the cannon. If the cannon is hoisted up to 4 times the height H, how much further will the cannonball fly before hitting the ground?

  1. Same distance
  2. Double the distance
  3. 4 times the distance
  4. 16 times the distance