1. The train entered the tunnel in 15 seconds. It took another 30 seconds for the last carriage to exit the tunnel. How long is the train and at what speed was it moving, if the tunnel is $300 \mathrm{~m}$ long.
Solution. The speed of the train is $10 \mathrm{~m} / \mathrm{s}$, and its length is $150 \mathrm{~m}$.