Question

5. A vehicle having a mass of 1000 kg had an accident on a wet, but level, concrete road under foggy
conditions. The tires were measured to have y = 0.55 on wet concrete. The driver locked the
brakes, skidded for 6 seconds, and then hit the guardrail causing a very small dent because the
vehicle stopped just as it touched the guardrail. The driver claimed to be driving 65 miles per hour
(29 m/s). You have been hired as an investigator to determine if the driver is telling the truth.
a. What is the weight of the vehicle?
b. The frictional force produces the negative acceleration that reduces the velocity of the
vehicle from its initial unknown speed to zero. Find the value of the frictional force.
Use the frictional force to calculate the acceleration (remember that it is a negative
number). Hint: Use Newton's 2nd Law.
d. Using your acceleration from partc, what was the driver's initial velocity? Hint: Use this
equation - The final velocity is 0 m/s.
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Answer 1

Answer:

Explanation:

1) weight = mg = 9.81*1000 = 9810 Newtons

2) frictional force = normal force *

we must assume that the vehicle is on a flat surface so therefore the normal force is the same as the weight of the vehicle.

frictional force = 9810 * 0.55 = 5 395.5 N

3) acceleration: F = ma, a = F/m

assume that only the frictional force is acting on the vehicle:

a = 5395.5/1000 = 5.3955 m/s

4) the car decelerates at 5.3955m/s

over 6 seconds, the car decelerates by: 32.37m/s

5) original speed = 29m/s final speed = 29-32.37 = -3.37m/s which is a negative number, therefore the vehicle would have stopped before it hit the rail.

6) to get to the rail, the vehicle would have had to be traveling at least 32.37m/s which is 72.41 mph