A student tosses a 2 kg ball into the air 4 meters above his hand. Ignoring air friction, what will be the magnitude of the velocity of the ball when it returns to his hand?

A 1 m/s
B 2 m/s
C 8 m/s
D 10 m/s

Question

A student tosses a 2 kg ball into the air 4 meters above his hand.  Ignoring air friction, what will be the magnitude of the velocity of the ball when it returns to his hand?

A	1 m/s
B	2 m/s
C	8 m/s
D	10 m/s

anonymous · Answer

$$v _{f}^{2}=v _{i}^{2}+2a \Delta x$$

anonymous · Answer

but you dont have any velocity

anonymous · Answer

hmm but actually I'm getting 8.85 as my answer

anonymous · Answer

would vf be 0?

anonymous · Answer

mgh=0.5mv^2

anonymous · Answer

potential energy = kinetic energy

anonymous · Answer

hmm ill try both equations!

anonymous · Answer

ans= 8.85

anonymous · Answer

they give the same answer so I think something is missing.

anonymous · Answer

wait so it doesnt matter which equation?

anonymous · Answer

no both give the same result.

anonymous · Answer

but Im not sure if the answer is correct since 9 isn't listed.

anonymous · Answer

okay would vf = 0 in @VeritasVosLiberabit

anonymous · Answer

vi = 0 you are trying to find vf

anonymous · Answer

the answer is supposed to be 8 so i guess thats close right?

anonymous · Answer

oh hah yeah my bad

anonymous · Answer

hmm but you dont round downward

anonymous · Answer

if it asks for 1 sigfig the answer should be 9.

anonymous · Answer

yeah im a little iffy about that but i can try asking my teacher that one tomorrow morning!

anonymous · Answer

either way the question might be wrong taking g= 9.81... my best answer could be 10 :)

anonymous · Answer

thanks you guys! ill ask my teacher to verify it

anonymous · Answer

you're welcome.