Engineering Board Exam Reviewer · Applications: Cooling, Heating, and Mixture Problems · medium

Coffee at 90° C is left in a 20° C room and cools to 80° C in 2 minutes. How many minutes after it was poured will it reach 50° C?

  1. 9.98 min
  2. 10.99 min
  3. 8 min
  4. 5.42 min

Answer

B. 10.99 min

Solution

T-20=70ekt. At t=2: 60=70e2k k= 12 67. Setting T=50: 30=70ekt t=2 (3/7)/ (6/7) 10.99 minutes.

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