Question

Two lovers are parked 10.0m from the edge of a cliff in a car whose mass, including that of the occupants is 100kg. A jealous suitor ties a rope to the car's bumper and a 50. kg rock to the other end of the rope. He then lower the rock over the edge of the cliff, and the car, which is in neutral, accelerates toward the edge.

b) What is the acceleration of the car towards the edge?
c) How long do the lovers have to apply the brakes before they go over the edge?

Answer 1

Hi! I recommend you just re-ask this question! Or maybe you already have, I don't know. But that gives everybody a chance to contribute!

If you post a new question or have one open, you can post the link to this one anyway!

Firstly, this problem is violent. And dramatic. And also a romance. Oscar nominee.



So, the car is in neutral... We can assume negligible friction, for simplicity... And we'll assume that the car is pulled straight forward, rather than down a little bit like in my picture.

So, looking at it, it makes sense that the force that pulls the car foward is the rock's weight. Rocks weight: gravitational force on the rock's mass.
\(F_{w,\text{rock}} = m_\text{rock}g\) where \(g\) is gravitational acceleration.

So the car is pulled forward with this force, \(m_\text{rock}g\).

Does that help, knowing the force? Of course! :) You know the mass of the car, and the mass and force have a physical relationship in \(F=ma\), like \(F_\text{car}=m_\text{car}a_\text{car}\). You have this:
\(m_\text{rock}g=m_\text{car}a_\text{car}\implies \dfrac{m_\text{rock}g}{m_\text{car}}=a_\text{car}\)

There is \(a_\text{car}\) for you.

As for the brakes, I think we'll need mor information. It does matter how good the brakes are, after all. If the brakes can't provide more friction force to overcome the boulder's weight, there's no hope for the couple.

Lemme guess - plot twist: break line is cut, because jealous suitor thought ahead, and so no breaking is possible.