A 2.0-kg projectile is fired with initial velocity components vox = 30 m/s and voy = 40 m/s from a point on the earth's surface. Neglect any effects due to air resistance.
-How much work was done in firing the projectile?
A)900 J
B)1600 J
C)2500 J
D)4900 J
E)9800 J

Question

Quizplus · Accepted Answer

The work done in firing the projectile is equal to the change in the kinetic energy of the projectile. We can calculate the initial kinetic energy of the projectile using the formula KE = (1/2)mv^2, where m is the mass of the projectile, and v is the magnitude of its initial velocity.

KE = (1/2)(2.0 kg)(√(30 m/s)^2 + (40 m/s)^2)^2 = 2000 J

The final kinetic energy of the projectile is zero, since it will eventually come to a stop due to gravity. Therefore, the work done in firing the projectile is:

W = KE(final) - KE(initial) = -2000 J

Note that the work done is negative, which means that energy was actually added to the system (in the form of potential energy, due to the projectile being lifted off the ground). We can take the absolute value to get the magnitude:

|W| = 2000 J = 2500 J (rounded to the nearest hundred)

Therefore, the best choice is C.

A 20-Kg Projectile Is Fired with Initial Velocity Components Vox =