acceleration, velocity problem

• Sep 28th 2007, 02:39 PM
rcmango
acceleration, velocity problem
The left ventricle of the heart accelerates blood from rest to a velocity of +22 cm/s.
(a) If the displacement of the blood during the acceleration is +2.1 cm, determine its acceleration (in cm/s2).
should be in cm/s2

(b) How much time does it take for the blood to reach its final velocity?
in seconds?

thankyou for looking at this.
• Sep 28th 2007, 09:48 PM
CaptainBlack
Quote:

Originally Posted by rcmango
The left ventricle of the heart accelerates blood from rest to a velocity of +22 cm/s.
(a) If the displacement of the blood during the acceleration is +2.1 cm, determine its acceleration (in cm/s2).
should be in cm/s2

(b) How much time does it take for the blood to reach its final velocity?
in seconds?

thankyou for looking at this.

We have unknown acceleration $a$ acting for unknown time $t$. Then:

$
v(t)=at
$

as the blood starts from rest, and displacement:

$
s(t)=at^2/2
$

hence substituting in the given final velocity and displacements we have:

$
22=at
$

and

$
2.1=at^2
$

Now you solve this pair of quations for $a$ and $t$ to answer the question

RonL
• Sep 28th 2007, 10:08 PM
ticbol
Quote:

Originally Posted by rcmango
The left ventricle of the heart accelerates blood from rest to a velocity of +22 cm/s.
(a) If the displacement of the blood during the acceleration is +2.1 cm, determine its acceleration (in cm/s2).
should be in cm/s2

(b) How much time does it take for the blood to reach its final velocity?
in seconds?

thankyou for looking at this.

The acceleration is constant.

Given:
Vo = 0
V final, Vf = 22 cm/sec
distance travelled, d = 2.1 cm

d = [(Vo +Vf)/2]*t
2.1 = [(0 +22)/2]*t
2.1 =11t
t = 2.1/11 = 0.191 sec -------------answer.

Vf = Vo +at
22 = 0 +a(0.191)
a = 22/0.191 = 115.2 cm/sdec/sec -------------answer.
• Sep 29th 2007, 04:21 AM
topsquark
Quote:

Originally Posted by rcmango
The left ventricle of the heart accelerates blood from rest to a velocity of +22 cm/s.
(a) If the displacement of the blood during the acceleration is +2.1 cm, determine its acceleration (in cm/s2).
should be in cm/s2

(b) How much time does it take for the blood to reach its final velocity?
in seconds?

thankyou for looking at this.

Actually, you can get the answer to part a) directly if you use
$v^2 = v_0^2 + 2as$

-Dan