# Instantaneous Velocity and Speed

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**Instantaneous Velocity and Speed**

IDE. The graph in is for an armadillo that scampers left (negative direction of x) and right along an x axis. (a) When, if ever, is the animal to the left of the origin on the axis? When, if ever, is its velocity (b) negative, (c) positive, or (d) zero?

lIE. (a) If a particle’s position is given by x = 4 – 121 + 3t2 (where t is in seconds and x is in meters), what is its velocity at t = I s? (b) Is it moving in the positive or negative direction of x just then? (c) What is its speed just then? (d) Is the speed larger or smaller at later times? (Try answering the next two questions without further calculation.) (e) Is there ever an instant when the velocity is zero? (I) Is there a time after t = 3 s when the particle is moving in the negative direction of x?

12P. The position of a particle moving along the x aXis is given n centimeters by x = 9.75 + 1.50t3, where I is in seconds. Calculate

( ) the average velocity during the time interval t = 2.00 s to t =

3 0 s: (b) the instantaneous velocity at t = 2.00 s; (c) the instantaneous

v loy at t = 3.00 s; (d) the instantaneous velocity at t = 2.50 s: and.Ie) the instantaneous velocity hen the particle is midway between its positions at t = 2.00 sand’ t = 3.00 s. (f) Graph x versus I and indicate your answers graphically.

13P. How does the runner whose velocity-time graph is shown in 16 s? itw