- #1
FaraDazed
- 347
- 2
Homework Statement
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
Homework Equations
[itex]
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\\
[/itex]
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.
[itex]
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
[/itex]
The figures I got just seem low to me, any help or advice/pointers is greatly appreciated.