A 14-kg dog jumps up in the air to catch a ball. The dog's center of mass is normally 0.20 m above the ground, and he is 0.50 m long. The lowest he can get his center of mass is 0.10 m above the ground, and the highest he can get it before he can no longer push against the ground is 0.60 m .If the maximum force the dog can exert on the ground in pushing off is 2.1 times the gravitational force Earth exerts on him, how high can he jump?

Respuesta :

Answer:

1.29 m

Explanation:

Net force acting on the dog, [tex]F_net[/tex] will be given by

[tex]F_net=F_upward – F_downward=2.1F_g –F_g=2.1mg-mg=1.1(mg) [/tex] where m is mass and g is acceleration due to gravity

Since the work done by the net force against the ground equals the final potential energy

[tex]\triangle W=\triangle PE[/tex]

[tex]F_net \triangle x=mg(\triangle y)[/tex]

[tex]1.1mg(x-\hat x)= mg(\triangle y)[/tex]

[tex]1.1(x-\hat x)=\triangle y[/tex]

[tex]1.1(0.5 m-0.1 m)=\triangle y[/tex]

[tex]1.1(0.4 m) =\triangle y[/tex]

[tex]\triangle y =0.44 m[/tex]

Height which the dog can jump, [tex]h=x+\triangle y[/tex]

H=0.6+0.44=1.04 m

Total height to reach=Height to jump+ half height of the dog

=1.04 m+0.5(0.5 m)=1.29 m

He can jump "1.29 m" high.

Gravitational force:

According to the question,

The net force on dog be:

→ [tex]F_{net} = F_{upward} \ \hat a \ F_{downward}[/tex]

          [tex]= 2.1 F_g \ \hat a \ F_g[/tex]

          [tex]= 2.1 \ mg- mg[/tex]

          [tex]= 1.1(mg)[/tex]

We know the relation,

→   [tex]\Delta W = \Delta PE[/tex]

[tex]F_{net} \Delta x= mg (\Delta y)[/tex]

By substituting the values,

        [tex]1.1 mg(x-\hat x) = mg(\Delta y)[/tex]

[tex]1.1 (0.5 \ m -0.1 \ m) = \Delta y[/tex]

            [tex]1.1\times 0.4 m= \Delta y[/tex]

                        [tex]\Delta y = 0.44 \ m[/tex]

Now,

The height which the dog can run will be:

→ [tex]h = x+ \Delta y[/tex]

     [tex]= 0.6+0.44[/tex]

     [tex]= 1.04 \ m[/tex]

hence,

The total height be:

= Height to jump + Half height of the dog

= [tex]1.04+0.5(0.5)[/tex]

= [tex]1.29 \ m[/tex]

Thus the above answer is correct.

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