Isolated system....this homework is killing me...?

Question

I'm in desperate need of physics help. This problem is complicated.

A particle of mass 0.5-kg is shot from P, 60m above the ground at an angle of theta. The particle has an inital velocity vector V(initial) with a horizontal component of 30 m/s. The particle rises to a mazimum height of 20m above P. Using the law of conservation of energy, determine a) the vertical component of vector V(initial), b) the work done by the gravitational force on the particle during its motion from P to the ground, and c) the horizontal and vertical components of the velocity vector when the particle reaches the ground.

Please...please....sigh.

Answer 1

Using the law of conservation of energy determin

a) the vertical component of vector V(initial)

It went up 20 meters, mgh = 1/2mV^2, solve for velocity

sqrt[2(9.8m/sec^2*20meters)] = v = 19.8m/sec

b) the work done by the gravitational force on the particle during its motion from P to the ground.

Maybe this is a trick question, I will take it at face value, when at P it is 60meters above the ground, the work of the gravity bringing it down from P is just mgh = 0.5kg*9.8m/s^2*20m=98J

c) the horizontal and vertical components of the velocity vector when the particle reaches the ground:

Horizontal velocity is constant at 30m/sec, nothing to calculate.

Verticle velocity, keep in mind that the object reached its maximum height at 80 meters high (ie from a verticle perspective is is at zero velocity at that point, and begins to fall, the terminal vertical velocity comes from the potential energy of
mgh = 0.5kg*9.8m/s^2*80m = 1/2 mV^2, solve for v

vertical velocity is 39.6 m/sec downward

please check for calculation errors.

Answer 2

I'll Try: No air friction, right? Then the horizontal component upon impact with the ground will be unchanged: 30 m/s.
Vertically, gravity has slowed the projectile to a stop (W =.5 k. x 20m.) and hauled it down to the ground (W+.5k x 80m.)

I think the initial vert. component is the opposite (vert.) / the adjacent (horizontal)... the tangent of theta times 30 m/s.

Answer 3

yea this jogs my memory of that loopy Muslim at the navy base that killed fellow infantrymen we do not listen something approximately this how come? is that this Muslim detailed or some thing like obama ??..