Thursday

August 28, 2014

August 28, 2014

Posted by **Andrew** on Thursday, January 17, 2013 at 7:26pm.

Sally applies 32 N of force at an angle of 22 degrees above the horizontal to a 12 kg crate.

Ignoring friction, calculate the horizontal acceleration of the crate?

Conceptual: will the acceleration of the crate increase or decrease if the same force is applied at an angle of 16 degrees? Explain.

- Physics -
**Anonymous**, Thursday, January 17, 2013 at 7:55pmStart with a picture if you don't already have one and then draw a free body diagram (a dot with arrows to represent all the forces applied to the box if you dont know what that is go ahead and google it- it'll make sense if you see a picture). We can assume up and the direction of the applied force (F) is positive.

Forces in the y direction:

+Fn (normal force)

-mg (mass*gravity)

-F*sin(theta)

Fsin(theta) is the componet of the applied force in the y direction. If you remember the trig identites sin(theta)=opposite/hypotenuse. Here, the applied force is the hypo. so you get Fsin(theta)= the y component of the applied force since it is ppposite the angle at which the force is applied to the box.

X direction:

+Fcos(theta)

This is the same as the y component of the applied force except its the adjacent side to the angle and acts in the x direction.

Ok if that all made sense (I hope it did) now you're ready to write two equations, one in the x direction and one in the y, based on Newton's second law F=ma

Y direction:

Fn-mg-Fsin(theta)=ma

X direction:

Fcos(theta)=ma

Since you have all the information in the x direction substitute with numbers and solve for a. It should come out to be something around 2.47 m/s^2 if you rounded the same way I did.

PS if there was friction you would subtract its force from the x direction when using sum of forces = ma.

Hope this helps!

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