f.4 phy既野

adamsteve

咁你減速度低梗係要多D時間架 咁時間多左 DISTANCE點都係多左架=.=
繼續睇佢地混戰

...hUnG...

u=20m/s
v=0m/s
a=-10ms^-2
t=5s

s=ut+1/2at^2
s=20(5) + 1/2(-10)(5)
s=75m

if a change to 5 (smaller) , then:

u=20m/s
v=0m/s
a=-5ms^-2
t=5s

s=ut+1/2at^2
s=20(5) + 1/2(-5)5
s=87.5m

87.5m>75m , a longer distance is needed

if u take a is a postive value .


u=20m/s
v=0m/s
a=10ms^-2
t=5s


s=ut+1/2at^2
s=20(5) + 1/2(10)(5)
s=125m

a change to a smaller valuse:

u=20m/s
v=0m/s
a=5ms^-2
t=5s

s=ut+1/2at^2
s=20(5) + 1/2(5)5
s=112.5m

i dont know how to explain to u but
if  u take a is a positive value.
maybe then the s should be taken as a negative value :
-112.5m>-125m  
so longer dstance is needed?? - -"

cuz by v^2-u^2/2a..
if:
u=20m/s
v=0m/s
a=10ms^-2
t=5s

0^2-20^/2(10)
u'll also get the negative vlaue: -20m

piyopiyo

wow樓上寫咁多野好神