1.

In the arrangement shown in the fig. the ends P and Q color of a string are being moved downwards with a speed of v each. The pulleys are fixed. The mass M moves upwards with a speed of :

Answer»

`v/(costheta)`
`(2V)/(costheta)`
`vcostheta`
`2vcostheta`

Solution :As P and Q move downwards with same VELOCITY, the mass M moves UPWARDS and leng th of string I decreases at the rate of Vm`s^(-1)`

Here `l^(2) =y^(2) + a^(2)`
diff. w.r.t time,`:. 2l (DL)/(dt)=2y dy/dt +0`
since `(dl)/(dt)=v`
`:. (dy)/(dt)=1/y v`
Thus velocity of block `M=v/(costheta)`


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