我想問一條phy 數...

today1314

請問呢條數要點計???

Two objects A and B have masses mA and mB respectively.
The ratio of mA to mB is 1:4. The ratio of kinetic energy
possessed by A to that of B is 4:1.
Find the ratio of A's spped to B's speed.

shizuki_tsuyuki

mA/mB=1/4

0.5 mA (vA)^2:0.5 mB (vB)^2=4:1
mA(vA)^2/mB(vB)^2=4
1/4* (vA)^2/(vB)^2=4
(vA)^2/(vB)^2=16
vA/vB=4
vA:vB=4:1

today1314

我唔明點解0.5 mA (vA)^2:0.5 mB (vB)^2 會 =4:1
你可唔可以解釋吓??唔該

sapphire

The ratio of kinetic energy possessed by A to that of B is 4:1.

看不明這句嗎?

K.E. in A : K.E. in B = 4 : 1
K.E. = 1/2 m(v^2)

so that:
1/2 mA (vA)^2 : 1/2 mB (vB)^2 = 4 : 1

where
mA = mass of A
vA = velocity of A
mB = mass of B
vB = velocity of B

應該不難明白吧?

today1314

我明la!! 好多謝兩位!!! ^_^