Answer:
141.94 cm³/s
Step-by-step explanation:
Since the volume of the tank V = πr²h, and both the height and radius of the tank change with time, we find the rate of change of the volume with time, dV/dt from
dV/dt = dV//dr × dr/dt + dV/dh × dh/dt
where dV/dr = 2πrh, dr/dt = + 0.2 cm/s (since the radius of the tank expands), dV/dh = πr² and dh/dt = -0.5 cm/s (since the height of the tank decreases)
So,
dV/dt = dV/dr × dr/dt + dV/dh × dh/dt
dV/dt = 2πrh × + 0.2 cm/s + πr² × -0.5 cm/s
dV/dt = 0.4πrh cm/s - 0.5πr² cm/s
dV/dt = πr(0.4h - 0.5r) cm/s
We now find the rate at which the volume is changing when r = 1.8 cm and h = 65 cm.
So,
dV/dt = π(1.8 cm)(0.4 × 65 cm - 0.5 × 1.8 cm) cm/s
dV/dt = π(1.8 cm)(26 cm - 0.9 cm) cm/s
dV/dt = π(1.8 cm)(25.1 cm) cm/s
dV/dt = π(45.18 cm²) cm/s
dV/dt = 141.94 cm³/s
