The stopping sight distance for a car traveling at 50 mph is 461 ft (including both perception-reaction distance and braking distance). The perception-reaction time is 2.5 sec. If a car traveling at 60 mph is to stop in the same distance with the same deceleration, what is most nearly the required perception-reaction time

2.08 s

Explanation:

We are given that

Speed,v=50mph=73.3ft/s

1 mile=5280 feet

1 hour=3600 s

Distance,d=461 ft

t=2.5 s

v'=60 mph=88 ft/s

We have to find the perception reaction time.

Perception reaction distance=

force is based upon mass and acceleration.the statement is not always true.

it can be explained from newton's second law of motion.

as per newton's second law of motion the rate of change of momentum is directly proportional to the applied force and takes place along the direction of force.

mathematically it can be written as -

                                              ⇒      

here   k is the proportionality constant whose value is 1.

                                                            [a is the acceleration=dv/dt]

hence we see that force not only depends on mass and acceleration but also on velocity and rate of change of mass. force f will depend on mass and acceleration only when mass is constant.

hence the statement that force is based upon mass and acceleration is false.