find kinetic energy

Question

When 75N of force is applied to a particular box, it will accelerate at 1.2 m/s2. This box is then loaded into a cannon and shot out. What is the kinetic energy of the box the instant it leaves the cannon if it is traveling at 400 m/s?

Answer 1

Given:

Fnet = 75 N

Acceleration = a = 1.2 m/s^2

Velocity = v = 400 m/s

Find:

KE = Kinetic Energy

Solution:

Apply Newton's 2nd Law to find the mass of the box

Newton's 2nd Law

Fnet = m*a

m = Fnet/a = 75/1.2 = 62.5 kg

Apply KE equation, which is a function of mass and velocity.

KE = (1/2) * m * v^2 = (1/2) * (62.5) * (400)^2 = 5x10^6 Joules (kg * m^2/s^2 = N*m)

Answer 2

You first determine the mass of the box using F = ma. Solve for m by substituting the given values for F and a.

Knowing m, use the KE equation 1/2 x m x V² where V is the given velocity.