Question

A train is 0.5 miles long and travels at a speed of 150 miles per hour. If the train crosses a bridge in 30 seconds, what is the length of the bridge?

• A. 0.5 miles
• B. 0.25 miles
• C. 0.6 miles
• D. 0.75 miles

Answer 1

The correct option is D 0.75 miles

Length of train = 0.5 mi

Speed of train = 150 mph

∴ Speed of train in miles per second $\text{will be}=\frac{150}{3600}=\frac{1}{24}$

So,
Distance covered in 30 s
$=\frac{1}{24}\times 30=\frac{5}{4}=1.25\text{mi}$

Since the train has to cover a combined distance of itself and the bridge to completely cross it, we can say:

$\text{Length of train + Length of bridge}=1.25$
$\Rightarrow 0.5+\text{Length of bridge}=1.25$
$\text{⇒Length of bridge}=0.75mi$

So, the length of the bridge is 0.75 miles.