A 2 kg rock is fired at an angle of 60 degree above the horizontal with an initial speed 20 m/s by someone standing on the edge of a cliff 40 m above level ground. The initial position of the rock is taken to be y = 0. Air resistance is not neglected in this situation!
(a) The initial mechanical energy of the rock is?
(b) The work being done on the rock by the force of gravity after
being fired and moving up through the air.
(c)At the highest point in the rock's trajectory, its mechanical
energy.
(d) The work being done on the rock by air resistance as it falls
down to the ground.
(a)
h = height at the point of launch = 40 m
m = mass of the rock = 2 kg
vi = speed of launch = 20 m/s
Initial mechanical energy is given as
TEi = mgh + (0.5) m vi2
TEi = (2 x 9.8 x 40) + (0.5) (2) (20)2
TEi = 1184 J
b)
At the highest point :
vf = final speed = vi Co60 = 20 Cos60 = 10 m/s
W = work done by gravity
Using conservation of energy
W = Change in kinetic energy
W = Final Kinetic energy - Initial kinetic energy
W = (0.5) m (vf2 - vi2) = (0.5) (2) ((10)2 - (20)2) = - 300 J
c)
Mechanical energy at the highest point is given as
TEf = TEi = 1184 J
A 2 kg rock is fired at an angle of 60 degree above the horizontal with...
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