{"id":229359,"date":"2025-06-08T06:33:03","date_gmt":"2025-06-08T06:33:03","guid":{"rendered":"https:\/\/learnexams.com\/blog\/?p=229359"},"modified":"2025-06-08T06:33:05","modified_gmt":"2025-06-08T06:33:05","slug":"a-runner-outputs-120-w-of-useful-power-during-a-90-minute-race","status":"publish","type":"post","link":"https:\/\/www.learnexams.com\/blog\/2025\/06\/08\/a-runner-outputs-120-w-of-useful-power-during-a-90-minute-race\/","title":{"rendered":"A runner outputs 120 W of useful power during a 90 minute race."},"content":{"rendered":"\n
A runner outputs 120 W of useful power during a 90 minute race. Express the total energy used in Joules and kW-h. a. 0.12 kW-h b. 0.18 kW-h c. 1.33 kW-h d. 1.8 kW-h<\/p>\n\n\n\n
The Correct Answer and Explanation is:<\/mark><\/strong><\/p>\n\n\n\n
To find the total energy used by the runner, we use the formula:Energy=Power\u00d7Time\\text{Energy} = \\text{Power} \\times \\text{Time}Energy=Power\u00d7Time<\/p>\n\n\n\n
Step 1: Convert Units<\/h3>\n\n\n\n
\n
Power is already given: 120 watts (W)<\/li>\n\n\n\n
Step 3: Convert Joules to kilowatt-hours (kW-h)<\/h3>\n\n\n\n
We know:1\u2009kW-h=3,600,000\u2009J1 \\, \\text{kW-h} = 3,600,000 \\, \\text{J}1kW-h=3,600,000J<\/p>\n\n\n\n
So:Energy in kW-h=648,000\u2009J3,600,000\u2009J\/kW-h=0.18\u2009kW-h\\text{Energy in kW-h} = \\frac{648,000 \\, \\text{J}}{3,600,000 \\, \\text{J\/kW-h}} = 0.18 \\, \\text{kW-h}Energy in kW-h=3,600,000J\/kW-h648,000J\u200b=0.18kW-h<\/p>\n\n\n\n
\n\n\n\n
\u2705 Correct Answer: b. 0.18 kW-h<\/strong><\/h3>\n\n\n\n\n\n\n\n
Explanation<\/h3>\n\n\n\n
Energy and power are fundamental concepts in physics. Power is defined as the rate at which work is done or energy is transferred. In this case, the runner outputs a useful power of 120 watts over the course of a 90-minute race. To find the total energy used, we must multiply power by the time for which it is used.<\/p>\n\n\n\n
However, it’s crucial to use consistent units. Power is given in watts, a unit in the International System (SI) equal to joules per second. The time must therefore be converted from minutes to seconds. Since there are 60 seconds in a minute, 90 minutes is 5400 seconds. Multiplying 120 watts by 5400 seconds yields 648,000 joules of energy.<\/p>\n\n\n\n
While joules are the SI unit of energy, energy is often also expressed in kilowatt-hours (kW-h), especially in electrical and utility contexts. One kilowatt-hour equals 3.6 million joules. To convert joules to kilowatt-hours, we divide the total energy in joules by 3,600,000.<\/p>\n\n\n\n
So, 648,000 J divided by 3,600,000 J\/kWh equals 0.18 kWh.<\/p>\n\n\n\n
This tells us that the runner used 0.18 kilowatt-hours of energy during the entire 90-minute race. It\u2019s a small amount in household terms (a 1000 W appliance running for less than 11 minutes uses more), but it\u2019s significant in human metabolic terms. The calculation also underscores the efficiency and limited power output of the human body, which typically produces around 100 to 200 watts of sustained mechanical power.<\/p>\n\n\n\n
Thus, option (b) 0.18 kW-h<\/strong> is the correct and well-supported choice.<\/p>\n\n\n\n<\/figure>\n","protected":false},"excerpt":{"rendered":"
A runner outputs 120 W of useful power during a 90 minute race. Express the total energy used in Joules and kW-h. a. 0.12 kW-h b. 0.18 kW-h c. 1.33 kW-h d. 1.8 kW-h The Correct Answer and Explanation is: To find the total energy used by the runner, we use the formula:Energy=Power\u00d7Time\\text{Energy} = \\text{Power} […]<\/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-229359","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/229359","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=229359"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/229359\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=229359"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=229359"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=229359"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
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