A perfect cube shaped ice cube melts so that the length of its sides are decreasing at a rate of 2secin. Assume that the block retains its cube shape as it melts. At what rate is the volume of the ice cube changing when the sides are 7in each?
Q. A perfect cube shaped ice cube melts so that the length of its sides are decreasing at a rate of 2secin. Assume that the block retains its cube shape as it melts. At what rate is the volume of the ice cube changing when the sides are 7in each?
Volume Formula: Let's denote the side length of the cube as s (in inches). The volume V of a cube is given by the formula V=s3. We are given that the side length s is decreasing at a rate of 2 inches per second, which we can write as dtds=−2 in/sec (the negative sign indicates a decrease). We want to find the rate of change of the volume, dtdV, when s=7 inches.
Chain Rule Application: To find dtdV, we will use the chain rule from calculus, which allows us to relate the rates of change of different quantities. The chain rule tells us that dtdV=dsdV⋅dtds. We already know dtds, so we need to find dsdV first.
Finding dsdV: Differentiating the volume formula V=s3 with respect to s, we get dsdV=3s2. This derivative represents the rate of change of the volume with respect to the side length.
Substitute s=7: Now we can substitute s=7 inches into the derivative to find the rate of change of the volume when the side length is 7 inches. So, dsdV=3×(7in)2=3×49in2=147in2.
Calculate dV/dt: We can now use the chain rule to find dV/dt. We have dV/dt=(dV/ds)⋅(ds/dt)=147in2/sec⋅(−2in/sec)=−294in3/sec. The negative sign indicates that the volume is decreasing.
Final Result: The rate at which the volume of the ice cube is changing when the sides are 7 inches each is −294 cubic inches per second.
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