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2 Questions!

:mad: i dont have a clue how to do these questions:mad:

1) Tennis player hits ball vertically at speed of 10m/s how high does it go?


2)Stone is dropped from a window 5m high at what speed does it hit the ground?

:frown:

thanks in advance:smile:
I'll give you a hint. Use SUVAT equations. And use the fact that projectiles under free fall always have an acceleration or deceleration of g i.e. 9.8m/s2. And remember to use your signs carefully.
Reply 2
Avatar for welwyn
welwyn
or for the second one you could use the equation GPE = KE assuming no energy loss, then word out the speed from the KE
SUVAT equations :confused: Are they a level stuff? never heard of em could be coz we have bad teacher though!


welwyn i see what u mean by using GPE=KE but i dont know the mass so im kinda stuck :frown:

For both questions only way i know i could work em out is if i knew mass:redface:
Reply 4
Avatar for Robob
Robob
17
You dont need the mass, 0.5mv^2 = mgh
0.5v^2 = gh
h = 0.5v^2 / g

rearrange differently for second question, as you can see the mass cancels

suvat equations are: v = u + at etc (have you seen that equation)
Reply 5
Avatar for welwyn
welwyn
if GPE = KE then the mass cancels from both sides.

and about 1) - use v^2 = u^2 + 2as
ie
the final velocity squared = the initial velocity squared + (2 x accn. of freefall x distance)
so
0 = 100 + (2 x -9.81 x s)

This is the easiest way, but I can't instantly think of a way with the mass.

welwyn
For 1) i got 5-lol hope its correct:smile:

for 2) im still kinda confused:frown:

thanks again for help so far its REALLY been appreciated
Reply 7
Avatar for Mr power
Mr power
yer suvat equations are a level stuff
s= distance
v= velocity
u= initial velocity
a = acceleartion
anon234
:mad: i dont have a clue how to do these questions:mad:

1) Tennis player hits ball vertically at speed of 10m/s how high does it go?


2)Stone is dropped from a window 5m high at what speed does it hit the ground?

:frown:

thanks in advance:smile:


Use the equation v^2=u^2+2as

where v = final velocity
u = initial velocity
s = displacement
a = acceleration (9.81 m/s/s)

So

1) rearrange teh equation to make s the subject, u=10m/s, v = 0 m/s and a = 9.81 m/s/s

s = (v^2-u^2)/2a
= (0 - 100) / 19.62
= 5.1m (if you ignore the '-' sign)

2) use the normal equation v^2 = u^2 + 2as v = subject, u = 0 a = 9.81 s = 5

v^2 = 2*9.81*5
v^2 = 98.1
v = 9.9 m/s
Wow? These teachers are original. Studying GCSE Physics and would you believe it.... these questions came up in a homework task -10 years later!
how do you know that for question 1, u is equal to 10m/s?similarly for 2, how is s equal to 5?

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