Question

A driver on a leveltwo-lane highway observes a

truck completely blocking thehighway.The driver was able to stop

her vehicle only 20 ft. fromthe truck. If the driver was driving at

60mph, how far was she fromthe truck when she first observed

it?

Answer 1

Answer:

SSD = 565.54 ft

Explanation:

Given data:

driver speed = 60 mph

clear distance available to stop the truck on emergency can be calculated by using stopping sight distance

SSD = Lag distance  +  breaking distance

$SSD = vt + \frac{v^2}{2gf}$

let take comfortable acceleration rate as a =  11.2 ft/s^2

g =32.2 ft/s^2

a = fg

$f = \frac{11.2}{32.2} = 0.348$

speed is given as 60 mph

we know that 1 mile 5290 ft

i hr = 3600 sec

therefore v = 88 ft./s

from standard assumption time to reaction is taken as 2.5 sec

so $SSD  =  88 \times 2.5 + \frac{88^2}{2\times 32.3\times 0.348}$

SSD = 565.54 ft