# Homework Help: Checking mechanics reasoning

1. Nov 25, 2013

### BOAS

Hello,

i'd like to run my reasoning by someone for a mechanics question. I've not been well, so have missed a few sessions where the material was covered - this is (part of) my attempt to catch up.

1. The problem statement, all variables and given/known data

A dump truck is being filled with sand. The sand falls straight down from a rest height of 2.0m above the truck bed, and the mass of sand hitting the truck per second is 55kg. The truck is parked on the platform of a weigh scale. By how much does the scale reading exceed the actual weight of the truck and sand?

2. Relevant equations

3. The attempt at a solution[/b

The truck and sand has a w = mg, but am artificial reading is given due to the net force of the sand pouring into the truck.

p = mv

a = (vf - vi / Δt)

Ʃf = ma

Ʃf = m(vf - vi / Δt)

= (mvf - mvi) / Δt

Since the sand starts at rest, Ʃf = mvf / Δt

I can use v2 = u2 + 2as to find the sands velocity and plug it into the above. And then the force is by how much the weight reading exceeds the weight of the truck and sand.

I hope that's correct, but mechanics isn't my strong suit.

Thanks for taking a look!

2. Nov 25, 2013

### Staff: Mentor

Your formulae appear to outline the correct approach to the answer. But it won't be if you are using m as the weight of the truck.

3. Nov 25, 2013

### BOAS

It's the sand that provides the extra force, so it's the sands momentum i'm interested in.

Thanks for the feedback.