1. The table shows the times for runners in a 100 m dash.
Runner Time (s)
A 9.30
B 5.7
C 6.00
D 7.42
If each runner has the same mass, which runner has the greatest force?
—> Is the answer run A (9.30) ? (i just assigned each runner to be 60 kg and multiplied that by the times)
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2. Which machine is basically two inclined planes?
doorstep, ax, screw, ramp
—> is the answer doorstep? (since it’s a wedge)
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3. Four people (AD) push the same heavy ball 100 m along a track. According to the graph, who used the least force?
http://www.flickr.com/photos/[email protected]/12642302…
–> Is it person d?
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4. In the graph, which machine has the greatest mechanical advantage?
http://www.flickr.com/photos/[email protected]/12642661…
—> is the answer B?? (I’m actually not sure about this at all)
3 Answers

for question 1 I can say your answer isn’t true.
the runner who has passed the way in less time actually is stronger. and has the greatest force. In physics we can formulate this with :
x=(1/2)*a*t^2 while “a” is acceleration that is (a=F/m) .
in first formula we see that either less the time therefore more the acceleration. ( note “x” means distance is constant ). in the second formula you see that in equal mass, force (F) simply relates with “a”.
so B is true that is the least. (5.7 sec)
for question 2. I thought a lot but I didn’t find out an answer better than yours. but it’s a wedge that’s consist of 3 planes. if I tell “Ramp” is true. it’s a simple plane!
i hope that this helped you .
and I have a request : Please do me a favor. and correct my mistakes in English sentences in this answer. I’m learning English. My Physics and math are OK but I’ve learned them in my language and now I’m trying to state them in English. Please be patient about it.
for question 3. your answer is true. But Why?
by the definition of Power we can prove:
Power=work/time or P=W/t=F.d/t=F.V so we can certainly say that F is the slope of the PV line. so every line that has the less slope will have the less required force. we see that D has the less slope so this is true. and person “D” used the least force.
for question 4. we know that mechanical advantage is shown by R is just a Ratio of advantageous work divided by disadvantageous work. R=(A.W)/(D.W). disadvantageous work is the work done by friction.
so we can say. R=(Fe.d)/(Fr.d). take note that both forces have the same distance. so we can say: R=Fe/Fr and so this is the slope of the lines in graph. each line that has more slope has more mechanical advantage. so A is true. because of the most slope.
I hope this will help.

Its perfect

B.
ax
D {UR answer}
A