11. [1pt] 
A vacationer gets into his out-board motorboat and leaves a dock on a river bank for a day of fishing. Just as he turns upstream, he hears a splash but pays no attention and continues cruising at normal speed. 5.0 minutes later he realizes that his watertight lunchbox is missing. He then turns downstream, with the motor still set at cruising speed. He sights his lunchbox floating down the river and retrieves it at a point 3.0 km downstream of the dock. How long after turning around does he pick up his lunch? 
Answer: 
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You have 5 tries 

12. [1pt] 
A commuter train travels between two downtown stations. Because the stations are only 1.05 km apart, the train never reaches its maximum possible cruising speed. The engineer minimizes the time t between the two stations by accelerating at a rate a1 = 0.125 m/s2 for a time t1 and then by braking with acceleration a2 = -0.480 m/s2 for a time t2. Calculate the minimum time of travel t. 
Answer: