Figure shows three forces applied to a trunk that moves leftward by 3.00 m over a frictionless floor. The force magnitudes are F 1
​
=5.00 N,F 2
​
=9.00 N, and F 3
​
=3.00 N. and the indicated angle is θ=60.0 0
. During the displacement,
(a) what is the net work done on the trunk by the three forces?
(b) does the kinetic energy of the trunk increase or decrease?

Respuesta :

The net work done on the trunk by the three forces is 1.50J and the kinetic energy of the trunk will increase

The data given in the question is:  

F 1 =5.00N,

F2 =9.00N,

F3 =3.00N,

θ=60°

d=3m

Work done by each force can be found as  

We know that, work done by a force is given by:

W =F d cosϕ,

where ϕ is the angle between Force and displacement vectors.

F₁ is in the direction of the displacement.

So,

W₁=F₁dcosϕ

     =(5.00N)(3.00m)cos0°

     =15.0J.

Force  F₂ makes an angle of

ϕ ₂=180°−θ

     =180°  −60°

     =120°

with the displacement i.e. in negative x direction.

So,

W₂=F₂dcosϕ₂

      =(9.00N)(3.00m)cos120°

      =−13.5J.

Force  F₃ is perpendicular to the displacement.

So,  W₃=F₃dcosϕ

            =(3.00N)(3.00m) cos90°  

            =0J

Net Work done by three forces is  

As work is a scalar quantity, so total work done will be the algebraic sum of all the individual works.

So,  W=W₁+W₂+W₃

          =15−13.5+0

          =+1.50J.

According to Work energy theorem, total work done on a system equal the change in kinetic energy of the system.

Here, a positive work of 1.5 Joules is done on the trunk, so its Kinetic Energy will increase by 1.5 Joules.

Figure was missing it is attached with the answer

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