A galvanometer has a coil of resistance `100 Omega` and gives full scale deflection for 30 mA current. If it is to work as a voltmeter of 30 V, the resistance required to be added is

Options

A. `sqrt60 m//s`
B. `sqrt45 m//s`
C. `sqrt30 m//s`
D. `sqrt15 m//s`

Answer

B

Explanation

`(h)/(sqrt3) = tan 60^(@) rArr h_(1) = 3m`
`(h_(2) - h_(1))/(3sqrt3) = tan30^(@) rArr h_(2) - h_(1) = 3 rArr h_(2) = 6m`
Velocity of block just before collision at B `= sqrt(2gh) = sqrt(2 xx 10 xx 3) = sqrt(60) ms^(-1)`

For totally inelastic collision velocity of block along normal to BC becomes zero adn since there is no impulse along BC becomes zero adn since there is no impulse along BC so momentum (velocity) along BC remains unchanged
Speed of block just after collision
`v_(B) = sqrt(60) cos 30^(@) = sqrt(60) xx (sqrt3)/(2) = sqrt(45) ms^(-1)`