A police officer is called in for accident reconstruction. He measures 11-meter long skid marks and he knows that for that particular tire\/pavement combination, the coefficient of kinetic friction is 0.65. He also knows that the car was traveling at 3.5 m\/s just before impact (the end of the skid marks). What was the speed of the car before it began the skid? Convert this to miles per hour. (Note: 1 mile = 1609 meters).<\/p>\n\n\n\n
The correct answer and explanation is :<\/strong><\/mark><\/p>\n\n\n\n The speed of the car before it began the skid was 12.35 m\/s<\/strong>, which is approximately 27.63 miles per hour (mph)<\/strong>.<\/p>\n\n\n\n When a car skids, it loses speed due to friction between the tires and the road. The police officer uses physics principles to reconstruct the accident and determine the vehicle\u2019s speed before braking.<\/p>\n\n\n\n We use the kinematic equation: First, calculate the deceleration:<\/p>\n\n\n\n [ Now, use the kinematic equation:<\/p>\n\n\n\n [ [ [ [ Since ( 1 ) mile = ( 1609 ) meters and ( 1 ) hour = ( 3600 ) seconds,<\/p>\n\n\n\n [ Thus, the car was traveling 27.63 mph<\/strong> before it started skidding.<\/p>\n","protected":false},"excerpt":{"rendered":" A police officer is called in for accident reconstruction. He measures 11-meter long skid marks and he knows that for that particular tire\/pavement combination, the coefficient of kinetic friction is 0.65. He also knows that the car was traveling at 3.5 m\/s just before impact (the end of the skid marks). What was the speed […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[25],"tags":[],"class_list":["post-199343","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/199343","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/comments?post=199343"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/199343\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=199343"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=199343"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=199343"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}Explanation:<\/h3>\n\n\n\n
Step 1: Use the Kinematic Equation<\/strong><\/h4>\n\n\n\n
[
v^2 = u^2 + 2as
]
Where:<\/p>\n\n\n\n\n
Step 2: Solve for ( u )<\/strong><\/h4>\n\n\n\n
a = – (0.65 \\times 9.81) = -6.3765 \\text{ m\/s}^2
]<\/p>\n\n\n\n
u^2 = v^2 – 2as
]<\/p>\n\n\n\n
u^2 = (3.5)^2 – 2(-6.3765)(11)
]<\/p>\n\n\n\n
u^2 = 12.25 + 140.283
]<\/p>\n\n\n\n
u = \\sqrt{152.533} = 12.35 \\text{ m\/s}
]<\/p>\n\n\n\nStep 3: Convert to Miles per Hour<\/strong><\/h4>\n\n\n\n
u_{\\text{mph}} = 12.35 \\times \\frac{3600}{1609} = 27.63 \\text{ mph}
]<\/p>\n\n\n\n