Question

A 1.2-kg mass is projected from ground level with a velocity of 31.3 m/s at some unknown angle above the horizontal. A short time after being projected, the mass barely clears a 16-m tall fence. Disregard air resistance and assume the ground is level. What is the kinetic energy of the mass as it clears the fence

Answer 1

Answer:

The kinetic energy will be "399.65 J".

Explanation:

Given:

Mass,

m = 1.2 kg

Velocity,

v = 31.3 m/s

The total energy of mass will be:

⇒ $E=K+U$

or,

⇒ $E=.5mv^2+mgh$

By putting the values, we get

        $=.5(1.2)(31.3)^2+0$

        $=0.6\times 979.69+0$

        $=587.81 \ J$

Since,

The system's total energy is unchanged, then

⇒ $E=K+U$

or,

⇒ $E=K+mgh$

   $587.81=K+1.2(9.8)(16)$

   $587.81=K+188.16$

          $K=587.81-188.16$                

               $=399.65 \ J$