Final answer:
When parked uphill next to a curb, turn the front wheels away from the curb to prevent the vehicle from rolling into traffic. The observed frequency of an ambulance siren matches the actual frequency most closely when the ambulance is approaching you, due to the Doppler effect.
Step-by-step explanation:
When parked uphill next to a curb, your front wheels should be turned away from the curb. This way, if your vehicle starts to roll, the wheels will catch against the curb and help prevent it from rolling into traffic. It's a safety precaution to ensure that the vehicle doesn't move into an unsafe position.
In the case of the GRASP CHECK related to sound frequency, the correct answer would be a. when it is coming toward you. This is due to the Doppler effect which is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. When the ambulance with its siren blaring is coming toward you, the sound waves are compressed, and the observed frequency is higher than when it is moving away or when it is directly in front of you.