Question

The temperature at 12 noon was 9°C above zero. If it decreases at the rate of 3°C per hour until midnight, at what time would the temperature be 12°C below zero? What would be the temperature at midnight?​

Answer 1

Step-by-step explanation:

Rate of change of temperature = -3°C

Temperature at noon = 9°C

A) To find : At what time temperature would be 12°C below 0, i.e. -12°C

Change of temperature = [Final temp.] - [Initial temp.] = -12 - 9 = -21°C

As rate of change of temperature is -3 per hour, it would take  

-21/-3 hours for temperature to become -12°C

= 7 hours.

12 noon + 7 hours = 19:00 = 7 p.m.

B) To find : Temperature at midnight

No. of hours until midnight = 24:00 - 12:00 (noon) = 12 hours.

As rate of change of temperature is -3°C per hour,

Temperature change after 12 hours = 12 * -3 = -36°C.

Temperature at midnight = [initial] + [change] = 9°C + -36°C = -27°C

Hope this helps!