To find the net force acting on the slab of concrete, we can analyze the forces involved:
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The total pull force from the two workers is: \[ 225 , \text{N} + 225 , \text{N} = 450 , \text{N} \quad (\text{upward}) \]
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The gravitational force acting downward on the slab is: \[ 400 , \text{N} \quad (\text{downward}) \]
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The net force is calculated by subtracting the downward force from the total upward force: \[ \text{Net Force} = \text{Upward Force} - \text{Downward Force} = 450 , \text{N} - 400 , \text{N} = 50 , \text{N} \quad (\text{upward}) \]
Since the net force is positive (50 N), the slab of concrete will move upward.
Therefore, the correct response is: 50 N; the slab will move upward.