A man stands on a platform that is rotating at 3.8 rpm; his arms are outstretched and he holds a brick in each hand. The rotatio
nal inertia of the system consisting of the man, bricks, and platform about the central axis of the platform is 4.65 kg-m². By moving the bricks the man decreases the rotational inertia of the system to 3.4 kg-m².
(a) what is the resulting angular speed of the platform and
(b) what is the ratio of the new kinetic energy of the system to the original kinetic energy?
(a) what is the resulting angular speed of the platform and
(b) what is the ratio of the new kinetic energy of the system to the original kinetic energy?
2 answers:
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Answer:
The maximum height that the fish can jump is 2.19 m.
Explanation:
Hi there!
Please, see the attached figure for a better understanding of the problem.
The motion of the salmon is a parabolic one because when it jumps, it already has a horizontal velocity (see figure).
The position and velocity vectors of the salmon at a time t, can be calculated as follows:
r = (x0 + v0x · t, y0 + v0y · t + 1/2 · g · t²)
v = (v0x, v0y + g · t)
Where:
r = position of the salmon at time t.
x0 = initial horizotal position.
v0x = initial horizontal velocity.
t = time.
y0 = initial vertical position.
v0y = initial vertical velocity.
g = acceleration of gravity.
Looking at the figure, notice that at the maximum height, the vertical velocity is zero (because the velocity vector is horizontal). Using the equation of the vertical component of the velocity, we can obtain the time at which the salmon is at its maximum height:
vy = v0y + g · t
To find the initial vertical velocity, v0y, let´s look at the figure. Notice that the initial velocity is the hypotenuse of the triangle formed with the horizontal velocity and the vertical velocity. Then:
v0² = v0x² + v0y²
Solving for v0y:
v0y = √(v0² - v0x²)
v0y = √((6.75 m/s)² - (1.65 m/s)²)
v0y = 6.55 m/s
Now, using the equation of the vertical component of the velocity at the maximum height (vy = 0):
vy = v0y + g · t
0 = 6.55 m/s + (-9.8 m/s²) · t
-6.55 m/s / -9.8 m/s² = t
t = 0.67 s
Now, using the equation of the vertical position at t = 0.67 s, we can find the maximum height:
y = y0 + v0y · t + 1/2 · g · t²
y = 0 m + 6.55 m/s · 0.67 s + 1/2 · (-9.8 m/s²) · (0.67 s)²
y = 2.19 m
The maximum height that the fish can jump is 2.19 m.
