F= -2i + 3j
+ k
d = AB = 3i
+ 4j – 4k
w = ?
Solution:-
Here we
have to find the work done by the given force and as we have formula for work
done
w = f .
dcos(Ѳ) , work done is cross product .As given we have force and displacement
in vector form. We also know that for dot product :-
i . i cos(0) = i.i (1) = 1 , j . j = 1 , k . k =1 ,
i . j cos(90) = 0 , j . k = 0 , k . i = 0 { because cos(90) = 0 }
so we simply multiply i.i , j.j , k.k
So w = f . d
cos(Ѳ) = (i)(i)cos(0) + (j)(j)cos(0) + (k)(k)cos(0)
{Therefore
cos(0) = 1}
w=
(-2)(3) + (3)(4) + (1)(-4)
w = - 6
+ 12 – 4
w = -10
+ 12
w = 2 J
.
SI unit of work is (joule) same as of energy. So we
write joule with the value of work.
So for more such type of questions , visite my website at undergraduate entry test , important questions are also available there.
2
) One another
concept , work done is independent of path followed between two points in
gravitational field , So gravitational field is a conservative field . Conservative
forces are not dependent of path followed by object , while non – conservative forces are dependent
on path followed by object .
3
) Air friction can …………………… the time period of simple pendulum .
A ) Increase
, B
) Decrease ,
C ) Not effected by air friction , c ) None of these ,
Correct
Answer : - A )
Increase ,
4
) Greater the least count in measured
value , ……………… will be its accuracy .
A ) Greater , B ) Smaller ,
C ) Not effected , c ) None of these ,
Correct Answer : - A ) Greater ,
Now go to online quiz section and check your preparation by this link : -
