Final answer:
The time it takes for a car to decelerate from 30 km/hr to 0 km/hr with an acceleration of -5 km/hr² is 6 hours. However, the unit for acceleration seems to be unusual and may be a typo, as km/hr² is not commonly used for acceleration. If the acceleration were -5 m/s², the time would be calculated using converted velocity units and would result in a more realistic value for a car stopping scenario.
Step-by-step explanation:
To determine how long it takes for a car to decelerate from 30 km/hr to 0 km/hr with an acceleration of -5 km/hr², we use the formula for acceleration (a) which connects initial velocity (v0), final velocity (v), and time (t): a = (v - v0) / t. Here, we need to solve for t.
First, we should convert the velocities to consistent units. Since acceleration is given in km/hr², we can keep the velocities in km/hr. Therefore, we have: v0 = 30 km/hr, v = 0 km/hr, and a = -5 km/hr².
Plugging the known values into the acceleration formula, we get:
-5 km/hr² = (0 km/hr - 30 km/hr) / t
t = -30 km/hr / -5 km/hr²
t = 6 hr
However, as the units of time given for acceleration (-5 km/hr²) suggest an unusual and impractical unit for acceleration, to make the answer more realistic, we would normally want the acceleration unit to be something like m/s². This may indicate a misunderstanding or typo in the original question. Acceleration in terms of km/hr² does not translate directly to a practical acceleration value, as it suggests the speed changes by 5 km/hr for every hour the object continues to accelerate (which is a very slow rate of deceleration and not useful for such a short duration event).
If we assume that -5 km/hr² was instead supposed to be -5 m/s², then we would convert the velocities to m/s: 30 km/hr = 30 * (1000 m/3600 s) = 8.33 m/s. With these conversions, we would then solve for time using the correct units, getting a more plausible answer for the time required to stop the car.