Question

Please help, physics question:

Answer 1

Answer:

Kinetic energy (K.E) when it is 30.0 m above the ground is 30.84 J .

Explanation:

Given :

Mass of arrow , m = 0.155 kg .

Initial velocity , u = 31.4 m/s .

To Find :

Kinetic energy (K.E) when it is 30.0 m above the ground .

Solution :

Let , us assume upward direction be positive and downward direction is negative .

Now , by equation of motion :

$v^2-u^2=2as$

Here , $a=g=-9.8\ m/s^2$ ( Because acceleration due to gravity is in downward direction )

Putting all given values in above equation , we get :

$v^2-31.4^2=2\times -9.8\times 30\\\\v^2=31.4^2-588\\\\v^2=397.96\\\\v=19.95\ m/s$

Now , kinetic energy is given by :

$K.E=\dfrac{1}{2}mv^2$

Putting all values we get :

K.E = 30.84 J .