# A Narrow Escape: Examining a Near-Miss in San Francisco

• tnutty
In summary, while driving in San Francisco, the driver encountered a steep hill and a small boy chasing a ball. Despite slamming on the brakes, the car left a 50 ft long skid mark. A policeman gave the driver a ticket for speeding, pointing out the 25 mph speed limit on the street. Upon further examination, the driver determined that the street had an angle of 20° with the horizontal and the coefficients of static and kinetic friction were 0.80 and 0.60, respectively. Using the equation v^2-v0^2 = 2x(x-x0), the driver calculated a speed of 36 mph, proving their guilt.
tnutty

## Homework Statement

While visiting a friend in San Francisco, you decide to drive around the city. You turn a corner and find yourself going up a steep hill. Suddenly a small boy runs out on the street chasing a ball. You slam on the brakes and skid to a stop, leaving a skid mark 50 ft long on the street. The boy calmly walks away, but a policeman watching from the sidewalk comes over and gives you a ticket for speeding. You are still shaking from the experience when he points out that the speed limit on this street is 25 mph.
After you recover your wits, you examine the situation more closely. You determine that the street makes an angle of 20° with the horizontal and that the coefficient of static friction between your tires and the street is 0.80. You also find that the coefficient of kinetic friction between your tires and the street is 0.60. Your car's information book tells you that the mass of your car is 1570 kg. You weigh 130 lb, and a witness tells you that the boy had a weight of about 60 lbs and took 3.0 s to cross the 15-ft wide street. Will you fight the ticket in court?

## The Attempt at a Solution

i got x: Ffriction + Fx

=

0.6mgCos(theta)+mosin(theta)

Doing exam questions are a little dubious on the homework forum.

Besides you've shown no real effort.

Alright this an old exam question. Here is my progress :

use the equation v^2-v0^2 = 2x(x-x0)

by trig I figured out,

Fnet = F of friction + F of x direction

= 0.6mgCos(@)+mgSin(@)

so,

v^2 = 0, Vo^2 = ? ,

a = Fnet/m
=

g(0.6Cos(theta) +gsin(theta)).

so

Vo^2 = 2F/m(X-Xo)

= sqrt ( 2 (g(.6Cos(@) + sin(@))(15.14)

= 16.44m/s

So what does that translate to in mph?

Should you fight the ticket then?

that translates to 36mph. I am not sure if my logic is correct though, which
is why i wanted someone to check it.

IF this is correct then he is guilty.

tnutty said:
that translates to 36mph. I am not sure if my logic is correct though, which
is why i wanted someone to check it.

IF this is correct then he is guilty.

Yep. He should just mail in the fine and wait for his auto insurance rates to go up.

## What is the purpose of the study?

The purpose of the study is to examine a near-miss incident that occurred in San Francisco and determine the potential causes and consequences of the event.

## What is a near-miss?

A near-miss is an unplanned event that could have resulted in harm, loss, or damage, but did not due to timely intervention or sheer luck.

## What is the significance of studying near-misses?

Studying near-misses can help identify potential hazards and prevent future accidents or disasters. It can also provide valuable insights into the effectiveness of safety protocols and procedures.

## What was the methodology used in the study?

The study used a combination of data analysis, interviews with eyewitnesses and experts, and simulations to reconstruct the event and identify contributing factors.

## What were the main findings of the study?

The main findings of the study were that the near-miss was caused by a combination of human error, equipment failure, and inadequate safety protocols. It also revealed potential areas for improvement in safety procedures and emergency response protocols.

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