Two cars start from the same place at the same time and move along roads at right angles to each other. Their speeds are 54 km/hr and 72 km/hr respectively. What will be the distance between them after 20 seconds?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 500 m
The two roads are the arms of a right triangle, so the gap between the cars is its hypotenuse.
54 km/hr \(\displaystyle =54\times\frac{5}{18}=15\) m/s; in 20 s the first car goes \(15\times20=300\) m
72 km/hr \(\displaystyle =72\times\frac{5}{18}=20\) m/s; in 20 s the second car goes \(20\times20=400\) m
Distance between them \(=\sqrt{300^{2}+400^{2}}=\sqrt{90000+160000}=\sqrt{250000}=500\) m
The cars are 500 m apart.