Final answer:
The frictional force exerted on a stationary 20N block with a coefficient of static friction of 0.4 is a maximum of 8N. This frictional force would change if the block is in motion, where the coefficient of kinetic friction would need to be used instead.
Step-by-step explanation:
The question pertains to the topic of Static and Kinetic Friction within high school Physics. When a block weighing 20N is resting on a horizontal surface, and the coefficients of static and kinetic friction between the block and surface are given, the frictional force exerted can be determined based on whether the block is stationary or moving. Since the block is at rest, the maximum static frictional force that can be exerted is the product of the coefficient of static friction (μs) and the normal force (N). The normal force in this case is equal to the weight of the block, which is 20N.
Therefore, the maximum static friction force that can be exerted on the block is:
fs(max) = μs × N
fs(max) = 0.4 × 20N
fs(max) = 8N
This means that up to 8N of force can be applied to the block without causing it to move. Once the block begins to move, the frictional force would then be the kinetic friction force, calculated using the coefficient of kinetic friction (μk) and the normal force.