- #1

PeterPeter

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## Homework Statement

A 14kg mass is attached to one side of a vertical pulley and an 8kg to the other.

The 14kg mass is 5m above the ground. The 8kg is just resting on the ground. The pulley is frictionless and weightless.

Find the velocity of the 14kg mass just before it hits the ground.

## Homework Equations

F=ma;

v^2=u^2+2a*s where s is the distance

## The Attempt at a Solution

Draw a free body diagram for the 14kg mass. Take downwards as positive,

Let g= acceleration due to gravity. The the net force on the 14Kg body is

F=14g-8g Newtons (acting down).

The 14Kg accelerates downwards with acceleration, a, given by:

a=(14g-8g)/14 = 4.2 m/s^2

Thus, since the acceleration is constant:

v^2=0 + 2*a*5

v= 6.5 m/s

This doesn't agree with the answer given is 5.2 m/s^2! So where have I gone wrong?