Question

Difficulty: MediumNewton's Second Law (F=ma)

During a testing sequence, a heavy torpedo with a mass of 1,500 kg1,500 \text{ kg} is fired from a submarine tube. The launch mechanism applies a forward propulsive force of 45,000 N45,000 \text{ N}. If the water resistance creates a constant opposing drag force of 9,000 N9,000 \text{ N}, what is the initial acceleration of the torpedo?

Answer: 24 m/s^2

Answer

24
To find the acceleration, we first determine the net force acting on the torpedo. The forward propulsive force is 45,000 N45,000 \text{ N}, but water resistance pushes back with 9,000 N9,000 \text{ N}. Subtracting the opposing force gives a net force of 36,000 N36,000 \text{ N}. Using Newton's Second Law (F=maF = ma), we rearrange the formula to solve for acceleration (a=Fma = \frac{F}{m}). Dividing the net force (36,000 N36,000 \text{ N}) by the mass (1,500 kg1,500 \text{ kg}) results in an acceleration of 24 m/s224 \text{ m/s}^2.

Step-by-Step Solution

1
Calculate the net force (FnetF_{net}) acting on the torpedo.
Fnet=45,000 N−9,000 N=36,000 NF_{net} = 45,000 \text{ N} - 9,000 \text{ N} = 36,000 \text{ N}
The torpedo experiences forces in opposite directions, so the drag force must be subtracted from the forward thrust to find the total effective force.
2
Calculate the acceleration (aa) using Newton's Second Law.
a=Fnetm=36,000 N1,500 kg=24 m/s2a = \frac{F_{net}}{m} = \frac{36,000 \text{ N}}{1,500 \text{ kg}} = 24 \text{ m/s}^2
Newton's Second Law states that acceleration equals the net force divided by the mass.

Key Concept

Newton's Second Law (F=ma) and Net Force
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