Displacement and Velocity
What is an object's change in position?
What is displacement?
A ball initially at rest rolls down a hill and has an acceleration of +3.3 m/s/s. If it accelerates for 7.5 s, how far will it move during this time?
What is +93 m?
True or False: When a ball is thrown straight up, both its velocity and acceleration are zero at the top of its flight.
False! Explanation: The acceleration due to gravity is always down, while the velocity at the ball's peak is zero.
What does the area between a velocity vs. time graph and the horizontal axis represent?
What is displacement?
If an object is located 20 m to the right of the origin at 1:00 PM and later the object is located 30 m to the right of the origin at 2:00 PM, what is the displacement from 1:00 PM to 2:00 PM?
What is 10 m to the right?
True or False: A negative acceleration will slow down a negative velocity.
What is false?
(Explanation: If the acceleration and velocity are in the same direction, the velocity speeds up.)
A freely falling object is found to be moving downward at 18 m/s. If it continues to fall, two seconds later the object would be moving with a velocity of _____.
What is 38 m/s?
True or False: An acceleration vs. time graph with a horizontal line below the time axis represents an object slowing down constantly.
What is false?
(Explanation: The object could be speeding up if the velocity is also in the negative direction.)
True or False: If the average speed is zero, then the average velocity must be zero.
What is false?
(Explanation: If average speed is zero, distance must be zero, however, displacement and distance aren't always the same!)
A student is running through the hallway in front of a motion sensor. A velocity vs time graph is shown. What must the graph look like to show constant acceleration?
What is a velocity vs time graph with a constant slope?
True or False: A ball is dropped off a very tall building, and another ball is thrown upwards off the same building. The first ball has a greater acceleration than the second.
What is false?
Explanation: Each ball experiences the same constant acceleration due to gravity (9.8 m/s/s down)
True or False: If a position vs. time graph has a negative, constant slope, the acceleration must be negative.
What is false?
(Explanation: If the slope of a position vs. time graph is constant, the acceleration is zero.)
True or False: The average speed and the average velocity can have the same direction.
What is false?
(Explanation: Speed NEVER has a direction, but velocity does!)
Which of the following have a zero acceleration?
a. An airplane flying level due east at a constant 500 mph
b. Child jumping upwards on a trampoline
c. Ball thrown straight up at its highest point
d. Ball reversing direction after rolling up a straight track
What is a. An airplane flying level due east at a constant 500 mph?
An arrow is shot straight up in the air at an initial speed of 15.0 m/s. After how much time is the arrow heading downward at a speed of 8.0 m/s?
What is 2.35 s?
What is the shape of a position vs. time graph for an object traveling in the positive direction and speeding up?
What is a shwoop going upwards?
A bus travels from El Paso, Texas, to Chihuahua, Mexico, in 5.2 h with an average velocity of 73 km/h to the south. What is the bus’ displacement? (in meters)
What is 380,000 m south?
A car starting from +20m/s travels with a constant acceleration of -2.0 m/s/s. How far will the car go before it comes to a stop?
What is +100m?
An arrow is shot straight up in the air at an initial speed of 15.0 m/s. After how much time is the arrow heading downward at a speed of 8.0 m/s?
What is 2.35 s?
Describe (or draw) a velocity vs. time graph for an object thrown up in the air and caught at the same height.
What is a straight line with a negative slope, beginning above the horizontal axis and ending below the horizontal axis?