The instantaneous speed may change during the time interval. Average speed does

Question

The instantaneous speed may change during the time interval. Average speed does not show the speed variations. It can include stops. In both the average and instantaneous speed, we are talking about the rate at which distance is covered. Your car has cruise control. The instanteous speed of a car remains constant for 30 minutes at 30 km/hr. For the next 30 minutes the instanteous speed is 50 km/hr. You then stop for an hour so the speed is zero. Thus the average speed is Question 27 options: 50 km/hr 40 km/hr 30 km/hr 20 km/hr

Explanation / Answer

(i) From 0 seconds to 5, seconds the velocity stays at minus 8 meters per seconds, therefore the change in velocity over the 5 second time period is 0: 0 m/s/s From 5 to 15 seconds, the velocity increases from - 8 m/s to + 8 m/s, a total change of 16 m/s over a 10 second time period. The average acceleration is 1.6 m/s/s From 0 to 20 seconds, the velocity increases from -8 m/s to + 8 m/s, a total change of 16 m/s over a 20 second time period. The average acceleration is 0.8 m/s/s (ii) Instantaneous accelerations are the slopes of the graph at that point: at 0 seconds, the slope is 0 m/s/s at 10seconds, the slope is 1.6 m/s/s at 18 seconds, the slope is 0 m/s/s.

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