A crate of potatoes of mass \(18.0 \mathrm{kg}\) is on a ramp with angle of incline \(30^{\circ}\) to the horizontal. The coefficients of friction are \(\mu_{\mathrm{s}}=0.75\) and \(\mu_{\mathrm{k}}=0.40 .\) Find the frictional force (magnitude and direction) on the crate if the crate is sliding up the ramp.

Short Answer

Expert verified
Answer: The magnitude of the frictional force on the crate is 61.12 N, and the direction is downwards along the ramp.

Step by step solution

01

Calculate gravitational force

First, we need to find the gravitational force acting on the crate. The gravitational force (weight) can be calculated using the formula: \(F_g = m \times g\) where \(F_g\) is the gravitational force, \(m\) is the mass of the crate, and \(g\) is the acceleration due to gravity (approximately \(9.81 \, m/s^2\)). Given mass \(m = 18.0 \, kg\), we have: \(F_g = 18.0 \, kg \times 9.81 \, m/s^2 = 176.58 \, N\)
02

Calculate normal force

Now that we have the gravitational force on the crate, we can calculate the normal force acting on the crate. The normal force is perpendicular to the ramp surface and can be calculated using the formula: \(F_n = F_g \times \cos{\theta}\) where \(F_n\) is the normal force and \(\theta\) is the angle of inclination. Given angle \(\theta = 30^{\circ}\), we have: \(F_n = 176.58 \, N \times \cos{30^{\circ}} = 152.81 \, N\)
03

Calculate frictional force

To find the frictional force acting on the crate when it is sliding up the ramp, we can use the formula for kinetic friction: \(F_f = \mu_k \times F_n\) where \(F_f\) is the frictional force and \(\mu_k\) is the coefficient of kinetic friction. Given coefficient of kinetic friction \(\mu_k = 0.40\), we have: \(F_f = 0.40 \times 152.81 \, N = 61.12 \, N\) Since the crate is sliding up the ramp, the frictional force acts in the opposite direction, i.e., down the ramp. Therefore, the magnitude of the frictional force on the crate is \(61.12 \, N\), and the direction is downwards along the ramp.

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