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Motion In A Plane

Question
CBSEENPH11018449

The position of particle at any instant is given by straight r with rightwards arrow on top equals 50 straight t straight j with hat on top plus 5 straight t squared straight i with hat on topAt what instant the velocity vector will make an angle 45° with X-axis?

Solution

Given,
Position of the particle, straight r with rightwards arrow on top space equals space 50 straight t straight j with hat on top plus 5 straight t squared straight i with hat on top
∴ Velocity, straight v with rightwards arrow on top equals straight d over dt left parenthesis straight r with rightwards arrow on top right parenthesis space equals space straight d over dt left parenthesis 50 straight t space straight j with hat on top plus 5 straight t squared straight i with hat on top right parenthesis 
                 equals 50 straight j with hat on top plus 10 straight t space straight i with hat on top
The angle which the velocity vector makes with X-axis at any instant is,
tanθ space equals space straight v subscript straight y over straight v subscript straight x equals fraction numerator 50 over denominator 10 straight t end fraction 
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#2 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/FolderTreeStorageAndCache.class.php(110): com_wiris_util_sys_Store->mkdirs()
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#4 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/TextServiceImpl.class.php(59): com_wiris_plugin_impl_RenderImpl->computeDigest(NULL, Array)
#5 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/service.php(19): com_wiris_plugin_impl_TextServiceImpl->service('mathml2accessib...', Array)
#6 {main}</pre>
Therefore,
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#1 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/util/sys/Store.class.php(56): mkdir('/home/config_ad...', 493)
#2 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/FolderTreeStorageAndCache.class.php(110): com_wiris_util_sys_Store->mkdirs()
#3 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/RenderImpl.class.php(231): com_wiris_plugin_impl_FolderTreeStorageAndCache->codeDigest('mml=<math xmlns...')
#4 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/lib/com/wiris/plugin/impl/TextServiceImpl.class.php(59): com_wiris_plugin_impl_RenderImpl->computeDigest(NULL, Array)
#5 /home/config_admin/public/felixventures.in/public/application/css/plugins/tiny_mce_wiris/integration/service.php(19): com_wiris_plugin_impl_TextServiceImpl->service('mathml2accessib...', Array)
#6 {main}</pre>
rightwards double arrow          straight t equals 5 straight s
So, when time is 5 seconds, the velocity vector will make an angle 450 with x-axis.