Help: Force & acceleration

  • #1
1) A mass 1.3 kilograms is pushed with a horizontal force 17.5 Newtons of a smooth inclined plane which bears an angle 12.5 to the horizontal. Find the acceleration of the mass (g = 9.81 m/s).

I got 2.12, but it was wrong, and I don't know why.

2) A mass 1.9 kilograms is pushed with a horizontal force 20 Newtons of a smooth inclined plane which bears an angle 27 to the horizontal. Find the distance the block moves in 6.5 seconds (g= 9.81 m/s2).

I got 198.13, but it was wrong, and I don't know why.
 

Answers and Replies

  • #2
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buffgilville said:
1) A mass 1.3 kilograms is pushed with a horizontal force 17.5 Newtons of a smooth inclined plane which bears an angle 12.5 to the horizontal. Find the acceleration of the mass (g = 9.81 m/s).

I got 2.12, but it was wrong, and I don't know why.

This is a matter (also for the second question) of using the right components of given forces. The given force is HORIZONTAL so you need the component of this force in the direction that the object moves: 12.5 degrees upwards.

F = ma so that a=F/m and F = 17.5*cos(12.5)

I get 13.1 m/s² for this one

Then there is gravity F =m*g pointing down vertically. The component of this force along the inclination is -m*g*sin(12.5). And minus because it points DOWN the y-axis...so the acceleration here is -2.1 m/s²

So I get : 13.1 - 2.1 = 11 m/s² as an anwser...

marlon

same thing for the second question : draw a sketch and call the inclination the x-axis...
 

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