# Homework Help: Constant Acceleration and Resolution of Forces

1. Feb 20, 2013

1. The problem statement, all variables and given/known data
A block of concrete 5kg is initially at rest on a smooth (frictionless) horizontal surface. It is then pulled along by a constant force A, inclined at 45° from the horizontal. In the first 5 seconds of motion, the block moves a distance of 10m.

A: Find the acceleration of the body
B: Find the magnitude of the force A
C: Find the normal reaction force

2. Relevant equations
$v=u+at\\ s=\frac{1}{2}(u+v)t\\ s=ut+\frac{1}{2}at^2\\ v^2=u^2+2as\\ F=ma\\ R=mg\\$

3. The attempt at a solution
I wasn't quite sure how to start but with the known variables I started with equation 2 from above and then the rest is dependent of whether I started it correctly.
$Part A:\\ s=\frac{1}{2}(u+v)t\\ 10=0.5(0+v)5\\ 10=2.5v\\ v=4\\ .\\ v=u+at\\ 4=0+a5\\ a=\frac{4}{5}=0.8\\ .\\ Part B:\\ Acos45=ma\\ Acos45=5 \times 0.8\\ 0.71A= 4\\ A=\frac{4}{0.71}=5.63N\\ .\\ Part C:\\ R+Asin45=mg\\ R+5.63sin45=5 \times 9.8\\ R+3.98=49\\ R=49-3.98=45.02N$

The figures I got just seem low to me, any help or advice/pointers is greatly appreciated.

2. Feb 20, 2013

### Staff: Mentor

Looks good to me.

3. Feb 20, 2013