Physics help?

If you go to the following website, you will see a drawing of a problem that is similar to this problem.

http://dev.physicslab.org/Document.aspx?doctype=3&...

In the drawing, the drawing, you can see that the weight of the box that is hanging from the pulley is the force that is causing both boxes to accelerate. To determine the acceleration of both boxes, use the following equation.

Weight of box B = Total mass * acceleration

Weight = 1.64 * 9.8 = 16.072 N

Net force = Total mass * acceleration

16.072 = 6.5 * a

a = 16.072 ÷ 6.5

This is approximately 2.47 m/s^2.

To determine the kinetic energy of box A, we need to determine its velocity when box B hits the hits the floor. Since both boxes will have the same velocity, let’s use the following equation to determine this velocity.

vf^2 = vi^2 + 2 * a * d, vi = 0, a = 16.072 ÷ 6.5 = 0.757 m

vf^2 = 2 * (16.072 ÷ 6.5) * 0.757

vf^2 = 3.743539692

vf = √3.743539692

This is approximately 1.935 m/s.

Let’s use this number to determine the kinetic energy of box A when box B hits the floor.

KE = ½ * 4.86 * 3.743539692= 9.096801252 J

Box B is not free falling to ground as Abigail assumed. That is the reason that you can’t use conservation of potential and kinetic energy to determine the answer to this problem. I hope the drawing and my work has helped you to know how to solve this type of problem. If you need my help in the future, make me one of your contacts. Your questions will come directly to my yahoo email address.

morrison60957@yahoo.com

Hi,

To answer this question, you have to realize that the total amount of energy in the system (the two boxes) remains constant if frictional effects are ignored. So the potential energy of box B is equal to the kinetic energy of box A. Therefore;

Ek (A) = Ep (B)

Ek (A) = mgh

= 1.64*9.81*.757

=12.18 J

Good luck with your studies!