Monthly Archives: December 2015

Physics: Linear Motion (Motion in one dimension)

In all of these problems, the up direction is positive, the down direction is negative. Let’s use a rounded value for the acceleration due to gravity: -10 m/s2.

  1. An astronaut in outer space throws a rock. The rock leaves her hand and travels toward the Milky Way at 10 m/s. Where is the rock 2 seconds later?
  2. The same astronaut is now on earth and throws the same rock toward the Milky Way – assume she throws the rock straight up and it leaves her hand with a speed of 10 m/s. Where is the rock 2 seconds later? What is the difference between situation 1 and situation 2?
  3. Imagine a shelf full of dishes. The shelf is above a counter. A person grabs a dish and lowers the dish to the dish to the counter. Describe the velocity and acceleration of the dish as it is moved from shelf to counter.
  4. At the same shelf of dishes and counter, a cat knocks a dish down and the dish falls to the counter and breaks. Describe the velocity and acceleration of the dish as it is moved from shelf to counter. Why does it break? What is the difference between situation 3 and situation 4?

Physics: Mechanical Equilibrium & Newton’s First Law

Which of these objects is at mechanical equilibrium:

  1. A seagull standing on top of a fence post.
  2. A car moving due south at 40 kilometers per hour.
  3. A water drop from a kitchen tap, just before it hits the surface of the sink.
  4. A rain drop from the sky, just before it hits the ground.
  5. A car as it enters the freeway, traveling from a surface road where the speed limit is 60 km/h to the freeway where the speed limit is 100 km/h. The driver’s foot is pressing the accelerator.
  6. A can in a factory on a conveyor belt moving at 0.1 m/s.
  7. A bicycle wheel rolling in a straight line at 50 revolutions per second.
  8. A coin after it is dropped from someone’s hand and before it hits the ground.
  9. A rock thrown up in the air, at the very top of its journey through the air.
  10. The earth as it travels around the sun. (This is a trick question, something to think about. Assume that the earth travels around the sun in a circle, and assume that the earth’s speed is constant. The earth’s orbit is approximately circular and its speed is approximately constant – after all, it goes around pretty steadily once a year.)

Answers