Vertical Displacement of an arrow?

[dm187]

1. An Arrow is aimed horizontally at a bulls-eye 15 m away. If the initial veoicity of the arrow is 128 km/hr, how far below the bulls-eye will the arrow strike?

A) 2.1 cm
B)12
C)42 cm
D)87 cm

2. Homework Equations :
x=a*t or t=x/a
y=1/2g*[t][/2]



3. So first, we convert 15 m and 128 km/hr to cm and cm/s respectively:
15m*100=1,500 cm
128 km/hr * 1000m/km * 100m/cm * 1hr/60min * 1min/60s= 3,555.5 cm/s

Next, I find how much time is elapsed:
t=1,500cm/3,555.5 cm/s
t=.42 s

Finally, I find vertical displacement:
First, convert gravity in m/s^2 to cm/s^2; 9.8m*100= 980cm
Now, y=(1/2)(980cm/s^2)*.42^2
y=86.436


So is the answer D?

Thanks in advance.

 

[Stonebridge]

1. An Arrow is aimed horizontally at a bulls-eye 15 m away. If the initial veoicity of the arrow is 128 km/hr, how far below the bulls-eye will the arrow strike?

A) 2.1 cm
B)12
C)42 cm
D)87 cm

2. Homework Equations :
x=a*t or t=x/a
y=1/2g*[t][/2]



3. So first, we convert 15 m and 128 km/hr to cm and cm/s respectively:
15m*100=1,500 cm
128 km/hr * 1000m/km * 100m/cm * 1hr/60min * 1min/60s= 3,555.5 cm/s

Next, I find how much time is elapsed:
t=1,500cm/3,555.5 cm/s
t=.42 s

Finally, I find vertical displacement:
First, convert gravity in m/s^2 to cm/s^2; 9.8m*100= 980cm
Now, y=(1/2)(980cm/s^2)*.42^2
y=86.436


So is the answer D?

Thanks in advance.

That's the correct method and the correct answer.

 

[dm187]

Alright, thanks for the confirmation.