A car is moving on straight highway with a speed of 108 km/h.

5.3333 sec

Explanation:

initial speed: u = 108km/hr or 30 m/s

final speed: v = 0m/s

distance travelled: s = 80m

time the car took to stop: = t sec

= 2as,

a = ()/2s

a = (0-900)/160

a = -5.625

v = u + at,

t = (v - u)/a

t= (0 - 30)/(-5.625)

t = 5.3333 sec

if the person is shown to have +90n, then ans is -10n.

if the person is shown to have -90n, then ans is +10n.