Physics 2133

Chapter 2

• Calculate the average velocity given the displacement and the elapsed time.
• Calculate the average acceleration given the change in velocity and the elapsed time.
• Solve problems in a constant-acceleration system.
• Define the following terms:
  
  • Displacement
  • Average velocity
  • Instantaneous velocity
  • Average acceleration
  • Instantaneous acceleration

Conceptual Questions

1. If the average velocity of an object is zero in some time interval, what can you say about the displacement of the object for that interval?
2. Can the instantaneous velocity of an object ever be greater in magnitude than the average velocity? Can it ever be less?
3. An outfielder throws a ball to home plate. What is true about the velocity and acceleration of the ball when the ball is at its highest?
4. A piece of lead is thrown upward at a velocity of 15 m/s. What is its velocity when it comes back down to the same height as it started?

Problems

1. An athlete swims the length of a 50.0-m pool in 20.0 s and makes the return trip to the starting position in 22.0 s. Determine her average velocities in (a) the first half of the swim, (b) the second half of the swim, and (c) the round trip.
2. Jules Verne in 1865 proposed sending men to the Moon by firing a space capsule from a 220-m long cannon with final velocity of 10.97 km/s. What would have been the unrealistically large acceleration experienced by the space travelers during launch? Compare you answer with the free-fall acceleration, 9.80 m/s.
3. A speedboat increases in speed from 20 m/s to 30 m/s in a distance of 200 m. Find (a) the magnitude of its acceleration and (b) the time it takes the boat to travel this distance.
4. A Cessna aircraft has a lift-off speed of 120 km/h. (a) What minimum constant acceleration does this require if the aircraft is to be airborne after a takeoff run of 240 m? (b) How long does it take the aircraft to become airborne?
5. A ball is thrown vertically upward with a speed of 25.0 m/s. (a) How high does it rise? (b) How long does it take to reach its highest point? (c) How long does it take to hit the ground after it reaches its highest point? (d) What is its speed when it returns to the level from which it started?
6. A model rocket is launched straight upward with an initial speed of 50.0 m/s. It accelerates with a constant upward acceleration of 2.00 m/s² until its engines stop at an altitude of 150 m. (a) What is the maximum height reached by the rocket? (b) How long after lift-off does the rocket reach its maximum height? (c) How long is the rocket in the air?

Solution