SPH 4U1
Physics Grade 12
Unit 2: Kinematics (How Things Move)
Note 2: Speed and Velocity
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Reference Text Section 1.1
Recall Definitions:
Scalar – magnitude and a unit (no direction)- time, distance, speed
Vector – point of reference, magnitude, unit & direction – positions, displacement, velocity
Speed – rate of change of distance with time
Displacement – the change of positions (final position – the intial position)
Velocity – rate of change of position with time
Instantaneous Velocity – speed at one point in time together with the direction it is moving in at that time.
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Example 1: A person jogs around a circular 800m track in 6 minutes. Calculate
(i) the average speed
(ii) the average velocity
Solution: Convert 6 minutes to seconds 6.0 min.* 60.0 s/min. = 360.0 s
(i) average speed =
(ii) average velocity =
Example 2: A clock has a 2nd hand that is 12.0 cm long. Find the following:
(i) Average speed of the tip of the 2nd hand
(ii) Instantaneous velocity as it passes the 6 & 9 on the clock face
(iii) Average velocity in moving from the 3 to the 12 on the clock
Solution:
(i)
(ii) (recall inst velocity is speed & dir’n at that point in time)
Speed is constant so
Answer: As it passes the 6 the inst. Velocity is 1.3 cm/s [LEFT]
Answer: As it passes the 9 the inst. Velocity is 1.3 cm/s [UP]
(iii) Find the displacement of the 2nd hand from 3 to 12
Do Section 1.1 Questions Page 17