Classical Mechanics
# Introduction to Forces

In the figure above, a block on a frictionless slope is hanging on a cord. The mass of the block is \(m= 4.0 \text{ kg}, \) and the slope makes a \( \theta=30 ^\circ \) angle with the horizontal. If the cord is cut, what is the magnitude of the acceleration of the block?

The gravitational acceleration is \( g= 10 \text{ m/s}^2. \)

In the movie *Spiderman 2*, there's a famous minute long scene where Spiderman stops a train. If the initial speed of a five-car, out of control subway train was around the top speed of the NYC subway (27 m/s), and Spiderman stopped the train in exactly one minute, then what is the magnitude of the force in **Newtons** that Spiderman exerted on the train as he stopped it?

**Details and assumptions**

- A standard New York City subway car full of terrified passengers has a mass of roughly 40,000 kg.
- You may assume the acceleration was constant and any other forces are negligible.

In the above diagram, two objects with their respective masses \(5\) kg and \(3\) kg are hung on a pulley with no friction. Find the magnitude of acceleration \((\text{in m/s}^2 )\) of the left object with mass \(5\) kg.

Gravitational acceleration is \(g = 10\) m/s\(^{2}\).

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