A truck tractor pulls two trailers, one behind the other, at a constant speed of 100 km/h. It takes 0.640 s for the big rig to completely pass onto a bridge 390 m long. For what duration of time is all or part of the truck-trailer combination on the bridge?

please show work

100km/h = 27.78m/s

390m / 27.78m/s = 14.038s

14.038 + 0.640s = 14.679s

The length of the tracktor with two trailers is

d=v•t= 27.78•0.64 = 17.78 m.
L=l+d=390+17.78=407.78m
Δt=L/v=407.78/27.78=14.68 s.

what does the L stand for?

To find the duration of time for which the truck-trailer combination is on the bridge, we need to first find the total distance traveled by the combination.

The time it takes for the big rig to completely pass onto the bridge is 0.640 s, and during this time, it travels a distance equal to the length of the bridge, which is 390 m.

Now, since the truck tractor pulls two trailers, the total length of the truck-trailer combination is three times the length of the big rig. Let's calculate the total distance traveled by the combination.

Total Distance = Length of the big rig + Length of two trailers
Total Distance = 390 m + 3 * 390 m (as the length of the big rig is equal to the length of one trailer)
Total Distance = 390 m + 1170 m
Total Distance = 1560 m

Therefore, the truck-trailer combination travels a distance of 1560 m.

Next, we can calculate the time it takes to cover this distance at a constant speed of 100 km/h.

We can convert the speed from km/h to m/s:
100 km/h = (100 * 1000) m/3600 s ≈ 27.78 m/s

Now, using the formula Time = Distance / Speed, we can find the duration of time for the entire truck-trailer combination to cover the distance:
Time = 1560 m / 27.78 m/s
Time ≈ 56.13 s

Therefore, the duration of time for which all or part of the truck-trailer combination is on the bridge is approximately 56.13 seconds.