Question

A car moving with a speed of 108 km/h is brought to rest in a distance of 60 m. The car's acceleration is -7.5 m/s/s. How much time did the car take to stop?

Answer 1

the stopping work is given by the kinetic energy of the car, so if I call with \(F\) the stopping force, and with \(d\) the space traveled by the car, then we can write:
\[Fd = \frac{1}{2}m{v^2}\]
now, we have that \(F=ma\) where \(a\) is the deceleration, so we can write:
\[mad = \frac{1}{2}m{v^2}\]
and finally:
\[d = \frac{{{v^2}}}{{2a}}\]

Answer 2

the requested time is given by the subsequent condition:
\[0 = v - at\]
please solve that equation for time \(t\). Of course \(v=108\;Km/h\)

Answer 3

@Michele_Laino

Answer 4

Thank you!!!!!!!!