Problem Solving 2

[learner27]

PLease check if my answers are correct"

 

Pyulo Pascual had abroken heart because he saw his beloved in a romantic mood with Zac Efron. So Pyulo jumped from top of the building

(a) What is the distance he fell in 1.5 sec?

(b) What was his speed after falling 10 m?

© HOw Long did it take him to fall 15 m?

 

my answers:

(a) 14.715m

(b) 10.03 m/s^2

© 3.06 sec.

 

thanks guys

[CaptainPanic]

Tell us how you did the calculations so far, because I have the feeling you're not using the correct formulas.

[learner27]

on a, i used Sy=1/2gt^2

on b, i used t=square root of 2Sy/g then

i solved for the acceleration a= Vf-Vi/t

then i solved for Sy=1/2gt^2

for c, i used , t=square root of 2Sy/g

[CaptainPanic]

on a, i used Sy=1/2gt^2

No, you didn't

You used Sy = g*t = 9.81 * 1.5 = 14.715, (which is wrong).

[learner27]

yeah my answer on a was my answer on b , sorry typo error.. my answer on a is 11.04m

i dont know how to get c ...

[CaptainPanic]

Sy = 0.5*a*t^2 + V0*t + S0

 

With the initial speed (V0) is zero, and we set the initial height (S0) also to zero, then we are left with:

 

Sy = 0.5*a*t^2 + 0 + 0 = 0.5*a*t^2

 

We know a = 9.81 m/s^2, and we know that Sy = 15 meters, because that's in the question.

Then you're left with 1 equation, and 1 unknown.

 

So, you have answer a now.

In b, I really don't know why you solve for the acceleration if you already know g (that's the gravity acceleration!). But the answer looks ok to me... you've rounded it off differently, I think.

And c is above.

 

It is easy to make mistakes with these formulas. If you have made a mistake, it is often easier to start again, on a fresh piece of paper. If you start to search for the mistake you might overlook it a million times. If you start fresh, you might just not make the mistake and you never have to search for it at all.

[learner27]

I Have my new answers!!! please check them for me:

 

a=11.04m

b=14.76m/s^2

c=1.75sec.

 

correct or still wrong?

[CaptainPanic]

b seems pretty close to what I get, but not exactly the same. Also, the question asks for a velocity (which has the unit m/s), and you write acceleration (m/s^2).

 

a and c correspond to what I had.

[learner27]

ok 14.01 ? yeah im sorry sir can i have another question im having a difficulty on

what is the formula that im going to use if the problem is looking for

speed and displacement, what should i use on speed and what for displacement?

because on my notes they have the same formula

(when i ask my teacher, he wont answer me clearly)

[CaptainPanic]

Yeah, that's more like what I had.

 

Displacement?? I don't know... I guess "displacement" could be a distance (the S you have). Not sure though... I have never really heard that word for that, but I am not a native English speaker.

 

Speed is the same as velocity.

[learner27]

Thank YOu So MUCH!