An object is thrown horizontally from the open
window of a building. If the initial speed of the
object is 20 m/s and it hits the ground 2.0 s later,
from what height was it thrown? (Neglect air
resistance and assume the ground is level.)
Initial vertical velocity = 0
formula: s = ut + (1/2)*g*t^2
s = 0 + 1/2*9.8*2^2
s = 9.8*2 = 19.6 m
Answer:
41°
Explanation:
Kinetic energy at bottom = potential energy at top
½ mv² = mgh
½ v² = gh
h = v²/(2g)
h = (2.4 m/s)² / (2 × 9.8 m/s²)
h = 0.294 m
The pendulum rises to a height of above the bottom. To determine the angle, we need to use trigonometry (see attached diagram).
L − h = L cos θ
cos θ = (L − h) / L
cos θ = (1.2 − 0.294) / 1.2
θ = 41.0°
Rounded to two significant figures, the pendulum makes a maximum angle of 41° with the vertical.
These two forces are called action and reaction forces and are the subject of Newton's third law of motion.
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