Final answer:
To calculate static friction, we find the normal force by multiplying the mass of the box by gravity, and then multiply by the coefficient of static friction. The normal force is 49 N, and thus the maximum static friction is 14.7 N. Since the applied force is 400 N, this is the force that will be overcome to start moving the box.
Step-by-step explanation:
The question asks us to calculate the static friction for a box of 5 kg on the floor when a force of 400 N is exerted, and the coefficient of friction is 0.3. To calculate the static friction, we must first determine the normal force (N). The normal force in this case is equal to the weight of the box, which is the mass (5 kg) times the acceleration due to gravity (approximately 9.8 m/s2). N = m × g = 5 kg × 9.8 m/s2 = 49 N. Now, we can use the coefficient of static friction (u) to find the maximum force of static friction (fs(max)): fs(max) = u × N = 0.3 × 49 N = 14.7 N. However, since the applied force is 400 N, and this value is considerably larger than the maximum static friction, the box would overcome the static friction and start to move. Therefore, the static friction in this scenario would be equal to its maximum value before the movement starts, which is 14.7 N.