a body of mass 1 kg is moving with velocity of ( 4i+3j ) m/s which changes to (-6i +2k ) m/s ,by a force .the work done by the force in changing the velocity is
a. 6 j
b. 10 j
c. 12.5 j
d. 7.5 j
Answers
Given : a body of mass 1 kg is moving with velocity of ( 4i+3j ) m/s which changes to (-6i +2k ) m/s by a force
To Find : the work done by the force in changing the velocity
a. 6 j
b. 10 j
c. 12.5 j
d. 7.5 j
Solution:
a body of mass 1 kg is moving with velocity of ( 4i+3j ) m/s
Initially
KE = (1/2)mv²
= (1/2) (1) ( 4i+3j ) . ( 4i+3j )
= (1/2) ( 16 + 9)
= 25/2
= 12.5
changes to (-6i +2k ) m/s
Finally
KE = (1/2)mv²
= (1/2) (1) ( -6i+2j ) . ( -6i+2j )
= (1/2) ( 36 + 4)
= (1/2)40
= 20
work done by the force in changing the velocity is = 20 - 12.5 = 7.5 Joule
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