6. A block of wood, which is 12.0 cm long, is dropped through an infrared sensor

Question

6. A block of wood, which is 12.0 cm long, is dropped through an infrared sensor designed to measure the time that the sensor is blocked. Assuming that this block of wood blocks the sensor for a time interval of 0.27 seconds, what is the speed of this block as it passes through the sensor? Is this speed “average” or “instantaneous”?

7. Suppose that in problem #6 above the length of the block is known to an accuracy of +/- 0.3 cm, while the timer is limited to an accuracy of +/- 0.05 seconds.
a. What is the maximum speed you would calculate for this block, based on these error limits?
b. How much does this maximum differ from the speed calculated in #6 above?

c. What is the minimum speed you would calculate for this block based on these error limits? d. How much does this minimum speed differ from the calculated speed in #6 above?
e. How do the maximum (b) error and the minimum (d) errors compare?

1. A race car, moving initially with a speed of 15.0 m/s, is capable of accelerating at a rate of 6.0 m/s2. What will be the speed of this car after accelerating for a time period of 8.00 seconds?

Explanation / Answer

1.

vo = initial velocity = 15 m/s

vf = final velocity = ?

t = time taken = 8 sec

a = acceleration = 6 m/s2

Using the equation

vf = vo + a t

vf = 15 + (6) (8)

vf = 63 m/s

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