Answer:
12.6 seconds
Explanation:
With respect to the gazelle, the cheetah has a relative speed of 100 - 80 = 20 km/hr.
We convert from km/hr to m/s.
[tex]\dfrac{20000\text{ m}}{3600\text{ s}} = \dfrac{50}{9}\text{ m/s}[/tex]
At this relative speed, the cheetah will overtake the gazelle in time t given by
[tex]v= \dfrac{d}{t}[/tex]
d is the distance and v is the relative speed.
[tex]t = \dfrac{d}{v} = \dfrac{70.0}{50/9} = 12.6\text{ s}[/tex]
