{"id":239389,"date":"2025-07-02T20:03:25","date_gmt":"2025-07-02T20:03:25","guid":{"rendered":"https:\/\/learnexams.com\/blog\/?p=239389"},"modified":"2025-07-02T20:03:27","modified_gmt":"2025-07-02T20:03:27","slug":"which-one-of-the-following-is-a-dimensionless-quantity","status":"publish","type":"post","link":"https:\/\/www.learnexams.com\/blog\/2025\/07\/02\/which-one-of-the-following-is-a-dimensionless-quantity\/","title":{"rendered":"Which one of the following is a dimensionless quantity"},"content":{"rendered":"\n<p>Which one of the following is a dimensionless quantity? (a) mass (b) weight (c) specific weight (d) Reynolds number<\/p>\n\n\n\n<p><strong><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-ast-global-color-6-color\">The correct answer and explanation is:<\/mark><\/strong><\/p>\n\n\n\n<p>The correct answer is <strong>(d) Reynolds number<\/strong>.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Explanation:<\/h3>\n\n\n\n<p>A dimensionless quantity is one that does not have any physical dimensions or units. It is a pure number obtained by dividing two quantities with the same units, so the units cancel out. Now, let\u2019s look at each option:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>Mass<\/strong>: Mass is a physical quantity that measures the amount of matter in an object. It has the dimension of mass (M) and is typically measured in kilograms (kg), which makes it a dimensional quantity. Therefore, mass is not dimensionless.<\/li>\n\n\n\n<li><strong>Weight<\/strong>: Weight is the force exerted by gravity on an object and is calculated as the product of the mass of an object and the acceleration due to gravity (W = m * g). Since weight is a force, it has dimensions of mass times acceleration, which corresponds to the dimension [M L T\u207b\u00b2] (where M is mass, L is length, and T is time). Hence, weight is not dimensionless.<\/li>\n\n\n\n<li><strong>Specific weight<\/strong>: Specific weight is the weight per unit volume of a substance. It is calculated by dividing the weight of an object by its volume. The formula is \u03b3=WV\\gamma = \\frac{W}{V}, where WW is the weight and VV is the volume. Since weight is dimensionful and volume has the dimension of length cubed, specific weight is not dimensionless.<\/li>\n\n\n\n<li><strong>Reynolds number<\/strong>: Reynolds number is used to predict the flow regime of a fluid (laminar or turbulent) and is defined as the ratio of inertial forces to viscous forces. The formula for Reynolds number is: Re=\u03c1uL\u03bcRe = \\frac{\\rho u L}{\\mu} where \u03c1\\rho is the fluid density, uu is the fluid velocity, LL is a characteristic length, and \u03bc\\mu is the dynamic viscosity. The units of density, velocity, length, and viscosity cancel out, leaving Reynolds number as a dimensionless quantity. This makes it the correct choice.<\/li>\n<\/ol>\n\n\n\n<p>Thus, <strong>Reynolds number<\/strong> is the only option that does not depend on physical dimensions and is dimensionless.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Which one of the following is a dimensionless quantity? (a) mass (b) weight (c) specific weight (d) Reynolds number The correct answer and explanation is: The correct answer is (d) Reynolds number. Explanation: A dimensionless quantity is one that does not have any physical dimensions or units. It is a pure number obtained by dividing [&hellip;]<\/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-239389","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/239389","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=239389"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/239389\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=239389"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=239389"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=239389"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}