At a given instant, block A is moving upwards with velocity of 5m/s, what is velocity of block B at that instant? Assume that the strings are inextensible and pulleys are frictionless.
A
15m/s↓
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B
15m/s↑
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C
10m/s↓
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D
5m/s↑
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Solution
The correct option is A15m/s↓
Since the string is inextensible, length of the string remains constant. Let l1, l2, l3 and l4 are the intercepts of the string. l1+l2+l3+l4=constant
Differentiating the above equation w.r.t time t, we get equation in terms of velocity i.e. ⇒−VA−VA−VA+VB=0 (Taking upward velocity to be negative and downward positive) ⇒−5−5−5+VB=0 VB=15m/s↓