f.4 physics~

2012-06-30 7:01 am

a box of mass 3kg slides on a rough horizontal surface with an initial speed of
2ms-1 , it travels a distance of 10m before coming to rest.

find the frictional force acting on the box as it slides

我想問點解就感
friction= ma 就得啦??

吾係net force = ma 咩??

回答 (1)

胡雪8°

2012-06-30 7:56 pm

✔ 最佳答案

Method 1 :

Assume that the direction of movement of the box is negative.

u = 2 m s⁻¹
v = 0 m s⁻¹
s = 10 m

v² = u² + 2as
(0)² = (2)² + 2a(10)
a = -0.2 m s⁻²

F = f (Only frictional force acts on the box)
m = 3 kg

F = ma
f = 3(-0.2)
f = -0.6 N

Frictional force = 0.6 N
(The direction of the frictional force is opposite the direction of movement.)

=====
Method 2 :

Workdone to overcome the frictional force = Loss in kinetic energy
fs = (1/2)mu²
f(10) = (1/2)(3)(2)²
Frictional force, f = 0.6 N

參考: 胡雪

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