Question

A 1.2-kg mass is projected from ground level with a velocity of 30 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:

$K_f$ = 351.84 J

Explanation:

Using the conservation of energy K:

$E_i = E_f$

so:

$\frac{1}{2}mv^2 = K_f + mgh$

where m is the mass, v the initial velocity, $K_f$ is the kinetic energy of the mass as it clears the fence, g the gravity and h the altitude.

Then, replacing values, we get:

$\frac{1}{2}(1.2kg)(30m/s)^2 = K_f + (1.2kg)(9.8m/s^2)(16m)$

solving for $K_f$:

$K_f$ = 351.84 J