Math Problem Statement

It is exactly 7:20:47 in the morning. Determine the angle between the second hand and the minute hand.

Solution

To solve this problem, we need to determine the angle between the second hand and the minute hand at exactly 7:20:47.

Step 1: Understanding the movement of the hands

  1. Minute hand:

    • The minute hand completes a full circle (360°) in 60 minutes. Therefore, for each minute, it moves: 360°60=6° per minute.\frac{360°}{60} = 6° \text{ per minute}.
    • Since the current time is 20 minutes and 47 seconds, we convert 47 seconds into a fraction of a minute: Total minutes=20+4760=20.7833 minutes.\text{Total minutes} = 20 + \frac{47}{60} = 20.7833 \text{ minutes}.
    • Therefore, the minute hand has moved: Angle of minute hand=20.7833×6=124.7°.\text{Angle of minute hand} = 20.7833 \times 6 = 124.7°.
  2. Second hand:

    • The second hand moves a full circle (360°) in 60 seconds. Therefore, for each second, it moves: 360°60=6° per second.\frac{360°}{60} = 6° \text{ per second}.
    • Since the current second is 47, the second hand is at: Angle of second hand=47×6=282°.\text{Angle of second hand} = 47 \times 6 = 282°.

Step 2: Calculate the angle between the two hands

To find the angle between the second and minute hands, subtract the two angles and ensure the result is between 0° and 180° (since angles on a circle larger than 180° would be measured in the smaller direction).

Difference=282°124.7°=157.3°.\text{Difference} = |282° - 124.7°| = 157.3°.

Thus, the angle between the second hand and the minute hand at 7:20:47 is approximately 157.3°.


Would you like further details or clarifications? Here are 5 related questions for practice:

  1. What would be the angle between the hour and minute hands at the same time?
  2. How would the angle change if the time was 7:20:15 instead of 7:20:47?
  3. Can you calculate the angle between the hour and second hands at 7:20:47?
  4. What is the total movement of the second hand from 0 seconds to 47 seconds in degrees?
  5. How long does it take for the minute hand to move 1 degree?

Tip: To find angles between clock hands, remember that the hands move in a predictable manner: the minute hand moves 6° per minute, and the second hand moves 6° per second.

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Math Problem Analysis

Mathematical Concepts

Clock Angles
Circular Geometry
Time Conversions

Formulas

Angle of minute hand = minutes × 6°
Angle of second hand = seconds × 6°
Difference = |Angle of second hand - Angle of minute hand|

Theorems

Angle difference on a clock
Full circle = 360°

Suitable Grade Level

Grades 9-10