Final answer:
When approaching a road that's blocked from view, proceed with caution. The frequency of an ambulance siren is higher when it approaches due to the Doppler effect. In the bicyclist's reference frame, a stationary observer appears to move in the opposite direction.
Step-by-step explanation:
When approaching a road that's blocked from view, it is crucial for safety to proceed with caution. For example, when you see a woman with a baby stroller or a dog running out with its tail between its legs, these can be unpredictable situations that require immediate attention and careful driving. The same level of caution should apply when driving and encountering an emergency vehicle like an ambulance with its siren on. The GRASP CHECK question you mentioned about the ambulance's siren frequency can be explained by the Doppler effect, which states that the observed frequency of a sound wave depends on the relative speed of the source and the observer. Therefore, the answer to that question would be a. when it is coming toward you because the frequency of the siren appears to increase as the ambulance approaches you due to the waves being compressed. As for the bicyclist passing by, in the reference frame of the bicyclist, you would appear to be moving to the left.