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PHY一問

一個尋找知識中的小伙子

2007-01-04 1:14 am

a mass A of 3kg, moving at a velocity of 6ms^-1 on a smooth, hotrizontal table. It hits a 4kg mass B, which is initially at rest. After the collision, A continues to move in the same direction at a speed of 2ms^-1. Then all the masses pass over a rought surface which is 9m long. the friction between each mass and the rough surface is 1N.
b)After the collision, find the distance travelled of B.
c)After the collision, find the distance travelled of A.
d)Will they collide again?

回答 (1)

用戶98449

2007-01-04 5:13 am

✔ 最佳答案

Let the velocity of B after collision be v ms-1
By Conservation of Linear Momentum for the whole system
(3)(6) = (3)(2) + (4)(v)
v = 3

(b)
By Newton's Second Law
Deceleration of B = 1 / 4 = 0.25 ms-2
Applying v2 - u2 = 2as
Distance travelled by B = (0 - 32 ) / (2)(-0.25) = 18m

(c)
By Newton's Second Law
Deceleration of A = 1 / 3 = 0.333 ms-2
Applying v2 - u2 = 2as
Distance travelled by A = (0 - 22 ) / (2)(-0.333) = 6m

(d)
Note that Distance travelled by B > Distance travelled by A
Hence, they will NOT collide again.

Hope the above information helps =)

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