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A block is placed on a rough slope inclined at 30° to the horizontal. The coefficient of static friction between the block and the surface is 0.8. If the frictional force acting on the block is 10 N, what is the mass of the block in kg? (Take g = 10 m/s²) [2004]

1. 1.6
2. 4.0
3. 2.0
4. 2.5

Correct answer: 2.0

Solution

To find the mass of the block, we can use the formula for static friction, which is the product of the coefficient of static friction and the normal force. The normal force on the slope can be calculated using the weight of the block, which is equal to mass times gravity. Given that the frictional force is 10 N and the coefficient of static friction is 0.8, we can set up the equation 10 N = 0.8 * (mass * g * cos(30°)). Solving this yields a mass of 2.0 kg.

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