Two people

Two straight lines cross at right angles. Two people start simultaneously at the point of intersection. John walking at the rate of 4 kph in one road, Jenelyn walking at the rate of 8 kph on the other road. How long will it take for them to be 20√5 km apart

Result

t =  5 h

Solution:

v1=4 km/h v2=8 km/h  s=20 5=20 5 km44.7214 km  v=v12+v22=42+824 5 km/h8.9443 km/h  t=s/v=44.7214/8.9443=5 hv_{1}=4 \ \text{km/h} \ \\ v_{2}=8 \ \text{km/h} \ \\ \ \\ s=20 \cdot \ \sqrt{ 5 }=20 \ \sqrt{ 5 } \ \text{km} \doteq 44.7214 \ \text{km} \ \\ \ \\ v=\sqrt{ v_{1}^2+v_{2}^2 }=\sqrt{ 4^2+8^2 } \doteq 4 \ \sqrt{ 5 } \ \text{km/h} \doteq 8.9443 \ \text{km/h} \ \\ \ \\ t=s/v=44.7214/8.9443=5 \ \text{h}



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