# Physics4-39 magnitude of its velocity after falling 10.0m

#### karush

##### Well-known member
a) what is its speed after falling to 2.00s
motion formula $v=u+at$
so
$v = 6.00 \dfrac{m}{s} + 9.81 \dfrac{m}{s^{\cancel{2}}}{2.00 \cancel{s}} = 27.6 \dfrac{m}{s}$
b) How far does it fall in 2.00s
distance formula $d= ut + \dfrac{1}{2}at^2$
so
$d=6.00\dfrac{m}{\cancel{s}}\cdot 2.00\cancel{s} + \dfrac{1}{2}\cdot 9.81 \dfrac{m}{s^{\cancel{2}}}{(2.00s)^2} =12.00m+19.62m=31.6m$
c) What is the magnitude of its velocity after falling 10.0m?
graph $a-t, v-t, \textit{ and } y-t$ graphs for the motion.

ok don't have book answer to these and a little ?? on c} and graph

#### skeeter

##### Well-known member
MHB Math Helper
a) what is its speed after falling to 2.00s
motion formula $v=u+at$
so
$v = 6.00 \dfrac{m}{s} + 9.81 \dfrac{m}{s^{\cancel{2}}}{2.00 \cancel{s}} = 27.6 \dfrac{m}{s}$
b) How far does it fall in 2.00s
distance formula $d= ut + \dfrac{1}{2}at^2$
so
$d=6.00\dfrac{m}{\cancel{s}}\cdot 2.00\cancel{s} + \dfrac{1}{2}\cdot 9.81 \dfrac{m}{s^{\cancel{2}}}{(2.00s)^2} =12.00m+19.62m=31.6m$
c) What is the magnitude of its velocity after falling 10.0m?
graph $a-t, v-t, \textit{ and } y-t$ graphs for the motion.

ok don't have book answer to these and a little ?? on c} and graph
What information does the original problem statement give prior to asking parts (a), (b), and (c)?

#### karush

##### Well-known member
4-39 A student throws a water balloon vertically downward from the top of a building. The balloon leaves the thrower's had with a speed of $6.00 m/s$ Air resistance may by ignored, so the water balloon is in free fall after it leaves the throwers hand

a) what is its speed after falling to 2.00s
motion formula is $v=u+at$
so
$v = 6.00 \dfrac{m}{s} + 9.81 \dfrac{m}{s^{\cancel{2}}}{2.00 \cancel{s}} = 27.6 \dfrac{m}{s}$
b) How far does it fall in 2.00s
distance formula $d= ut + \dfrac{1}{2}at^2$
so
$d=6.00\dfrac{m}{\cancel{s}}\cdot 2.00\cancel{s} + \dfrac{1}{2}\cdot 9.81 \dfrac{m}{s^{\cancel{2}}}{(2.00s)^2} =12.00m+19.62m=31.6m$
c) What is the magnitude of its velocity after falling 10.0m?
graph $a-t, v-t, \textit{ and } y-t$ graphs for the motion.

c) ????

#### skeeter

##### Well-known member
MHB Math Helper
4-39 A student throws a water balloon vertically downward from the top of a building. The balloon leaves the thrower's had with a speed of [FONT=MathJax_Main]6.00[/FONT][FONT=MathJax_Math]m[/FONT][FONT=MathJax_Main]/[/FONT][FONT=MathJax_Math]s[/FONT] Air resistance may by ignored, so the water balloon is in free fall after it leaves the throwers hand
(a) $v(t) = v_0 - gt$

$v(2) = -6 - g(2) = -25.6 \, m/s$

speed is $|v| = |-25.6| = 25.6 \, m/s$

(b) $\Delta y = v_0 t - \dfrac{1}{2}gt^2$

$\Delta y = -6(2) - \dfrac{1}{2}g(2^2) = -31.6 \, m$

(c) $v_f^2 = v_0^2 - 2g \Delta y$

$v_f = -\sqrt{(-6)^2 - 2g(-10)} = -15.2 \, m/s$

$|v_f| = 15.2 \, m/s$

#### karush

##### Well-known member
ok, much mahalo

look like I didn't subtract