Question

1. The total work done on a particle by a constant force F = (21+ 3j + 4k ) Nover a
displacement s = ( 5i + 7j + zk )m is zero. Find the value of z.​

Answer 1

Explanation:

The position vector of two points (−1,2,1) and (2,−3,1)

r

=(2+1)

i

^

+(−3−2)

j

^

+(1−1)

k

^

r

=(3

i

^

−5

j

^

+0

k

^

)m

F

=(

i

^

+3

j

^

+4

k

^

)N

The work done by the force,

W=

F

.

r

W=(

i

^

+3

j

^

+4

k

^

).(3

i

^

−5

j

^

+0

k

^

)

W=1×3+3×(−5)+4×0

W=3−15=−12J

The correct option is C.

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