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A2L Item 019

Meta-Information
Description: 
Identify velocity graph for cart on incline
Goal: 
Relating physical motion with graphical representation
Level: 
High School
Keywords: 
Acceleration
Keywords: 
Graphing
Keywords: 
Mechanics
Keywords: 
Velocity
Source: 
UMPERG

Which of the velocity vs. time plots shown below might represent the velocity of a cart projected up an incline?

Select one of the above or:

(7) None of the above

(8) Cannot be determined

Commentary

Answer

(3) or (4). Initially the cart has a non-zero velocity pointing up the incline. The speed of the cart decreases as it moves up the incline, reaching zero at its maximum height. The speed of the cart increases as the cart moves down the incline. The velocity at the bottom of the incline points down the incline. Graph (3)/(4) is correct if up/down the incline is taken as the positive direction.

Background

Students will often associate velocity time graphs with features of the terrain. Many will pick either (5) because they neglect the vector nature of velocity and think about the speed.

Questions to Reveal Student Reasoning

Is the velocity ever zero? Is the velocity ever positive? … negative? When? Is the velocity constant? How do you know?

Suggestions

Plotting the position vs. time may help students come up with the correct plot of velocity vs. time.