velocity time graphs

acceleration and slope

In a velocity-time graph, acceleration is represented by the slope, or steepness, of the graph line. If the line slopes upward, like the line between 0 and 4 seconds in the Figure 1.1, velocity is increasing, so acceleration is positive. If the line is horizontal, as it is between 4 and 7 seconds, velocity is constant and acceleration is zero. If the line slopes downward, like the line between 7 and 10 seconds, velocity is decreasing and acceleration is negative. Negative acceleration is called deceleration. Q: Assume that another sprinter is running the same race. The other runner reaches a top velocity of 9 m/s by 4 seconds after the start of the race. How would the first 4 seconds of the velocity-time graph for this runner be different from the Figure 1.1? A: The graph line for this runner during seconds 0-4 would be steeper (have a greater slope). This would show that acceleration is greater during this time period for the other sprinter.


plotting velocity against time

The changing velocity of the sprinteror of any other moving person or objectcan be represented by a velocity- time graph like the one in the Figure 1.1 for the sprinter. A velocity-time graph shows how velocity changes over time. The sprinters velocity increases for the first 4 seconds of the race, it remains constant for the next 3 seconds, and it decreases during the last 3 seconds after she crosses the finish line.

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the steepness of a line graph is called its slope.

-->  a. true

b. false

if a velocity-time graph is horizontal, then velocity is

a) increasing.

b) decreasing.

-->  c) not changing.

d) accelerating.

in the graph described in question 5, acceleration is

-->  a) zero.

b) positive.

c) less than 1.

d) none of the above

in the graph in question 8, acceleration between seconds 2 and 4 is 10 m/s.

a. true

-->  b. false

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