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Found in: Page 140

### Fundamentals Of Physics

Book edition 10th Edition
Author(s) David Halliday
Pages 1328 pages
ISBN 9781118230718

# The floor of a railroad flatcar is loaded with loose crates having a coefficient of static friction 0.25 of with the floor. If the train is initially moving at a speed of 48 km/h, in how short a distance can the train be stopped at constant acceleration without causing the crates to slide over the floor?

The distance is 36.23 m

See the step by step solution

## Step 1: Given

Coefficient of static friction,${\mu }_{s}=0.25$

Initial speed of the train, ${v}_{0}=48\mathrm{km}/\mathrm{h}=13.33\mathrm{m}/\mathrm{s}$

Final speed of the train,${v}_{f}=0\mathrm{m}/\mathrm{s}$

## Step 2: Determining the concept

The problem is based on Newton’s second law of motion which states that the rate of change of momentum of a body is equal in both magnitude and direction of the force acting on it. Use the Newton's 2nd law of motion to find the acceleration of the train and then by using the Kinematic equations of motion, find the distance travelled by train.

Formula:

## Step 3: Determining the distance

The frictional force acting on the train is given by,

${f}_{s}={\mu }_{s}N\phantom{\rule{0ex}{0ex}}={\mu }_{s}\left(mg\right)$

By using Newton's 2nd law along the horizontal direction,

This is the acceleration of the train.

Now, by using the Kinematic equation of motion,

${v}^{2}={v}_{0}^{2}+2as\phantom{\rule{0ex}{0ex}}s=\frac{{v}^{2}-{v}_{0}^{2}}{2a}\phantom{\rule{0ex}{0ex}}=\frac{-{\left(13.33\right)}^{2}}{2\left(\left(-0.25\right)\left(9.81\right)\right)}\phantom{\rule{0ex}{0ex}}=36.23m$

Therefore, the distance is 36.23 m.