Question

1.Tectonic plates are large segments of the earth's crust that move slowly. Suppose one such plate has an average speed of 4.5 cm per year.

    (a) What distance does it move in 42 seconds at this speed?
    m
    (b) What is its speed in miles per million years?
    mi/My

2.
(a) A car speedometer has a 3% uncertainty. What is the range of possible speeds when it reads 80 km/h?
km/h (lowest)
km/h (highest)
(b) Convert this to miles per hour.
mi/h (lowest)
mi/h (highest)

Answer 1

1.

a)

1 yr = 365 days = 365 x 24 hours = 365 x 24 x 3600 sec

V_avg = average speed = 4.5 cm /yr = 4.5 cm /yr = 4.5 (cm/yr) (1 m/100 cm) (1 yr/(365 x 24 x 3600 sec) )

V_avg = 4.5 (1/(365 x 24 x 3600 x 100)) m/s = 1.43 x 10^-9 m/s

t = time of travel = 42 s

distance travelled is given as

d = V_avg t = (1.43 x 10^-9) (42) = 6.01 x 10^-8 m

b)

1 mile = 1609.34 m = 160934 cm

1 million yr = 10⁶ yr

v_avg = average speed = 4.5 cm/yr = 4.5 (cm/yr) (1 mile/160934 cm ) (10⁶ yr / 1 million yr )

v_avg = 4.5 x 10⁶ /(160934) cm/million yr = 27.96 cm/million yr