# Physics Again!!

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Am sending the same question coz i can't find the first one on the message boards. So plz help me.

1. 'velocity is a vector quantity, and the kinetic energy of a body is equal to half its mass times the square of its velocity, so kinetic energy must also be a vector.' Comment on the correctness of this argument.

2. A trolley of mass 0.80kg runs freely, without accelerating down an inclined plane when the plane makes 5 degrees with the horizontal. Finad the force parallel to the plane resisting motion.

The answer for this question is 0.68N. But by calculation I can only find the driving force of the trolley which is 8cos5. It is the vetical component of the weight which gives 0.68N and it is not parallel to the plane. So how can I calculate the frictional force??
Plz help!!!

Kinetic energy is not a vector. It is proportional to the square of velocity, regardless of direction.

Since the trolley is not accelerating, the friction force exactly balances the component of the gravity force down the ramp, which is M g sin 5 = 0.68 N

• Physics Again!! -

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