Vector →a lies in x – y plane, has magnitude of 18 units and points in a direction 250° from positive x-axis. Vector →b has magnitude 12 units and points in positive z-axis. What is →c=→c×→b?
A
10 rev/s
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B
20 rev/s
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C
30 rev/s
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D
40 rev/s
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Solution
The correct option is D
40 rev/s
The angle between →a and →b is 90° as →a is in x – y plane and →b is along positive z.
∴ |→a| = |→a×→a|= ab sin 90°
⇒ c = ab = 18 units
Also, the direction of →c is perpendicular to →b as well as →a, and using the screw rule we can see that it points 160° from positive x-axis, making it 90° from →a , and from →b in the x – y plane.