Change in Kinetic Energy of block

In summary, the block begins with a kinetic energy of +178.22 J and comes to a stop after traveling 6 m. The friction force exerted on the block is -70.61 N.
  • #1
grouchy
73
0
A 4.5 kg block is set into motion up an inclined plane with an initial speed of 8.9 m/s. The block comes to a rest after traveling 6 m along the plane, which is inclined at an angle of 24 to the horizontal. Determine the magnitude of the change in the block's kinetic energy.

I tried Delta K= Work of the Force
so..

Delta K = mgh but I got it wrong.
 
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  • #2
Delta K = mgh
What is the value of h you have substituted in this equation?
 
  • #3
grouchy said:
I tried Delta K= Work of the Force
so..

Delta K = mgh but I got it wrong.
You don't need any such equation to answer the question. Instead: What's the initial KE? What's the final KE? What's the change?
 
  • #4
I did also try Delta K = 1/2mVf^2 - 1/2 mVi^2. The final is 0 since it is at rest and I got -178.222 for the initial. But that was also wrong
 
  • #5
rl.bhat said:
Delta K = mgh
What is the value of h you have substituted in this equation?

for h I user 6sin24.
 
  • #6
grouchy said:
I did also try Delta K = 1/2mVf^2 - 1/2 mVi^2. The final is 0 since it is at rest and I got -178.222 for the initial. But that was also wrong
The initial KE = + 178.22 J. The change in KE is negative. But note that they ask for the magnitude of the change. (So drop the negative sign.)
 
  • #7
ok, I get that now. Magnitude is just the number and not the sign.

But for the next part it says that (Assumed: The fristional force is constant. Determine the magnitude of the frictional force exerted on the block.)

do I use, Wf = DeltaK + DeltaU?
 
  • #8
grouchy said:
do I use, Wf = DeltaK + DeltaU?
That will work.
 
  • #9
I don't get it, I'm getting it wrong. a previous question asked for the change in potential energy which I got to be 107.623. So I think I'm using the wrong sign or something...

I tried -178.223 + 107.623 and got -70.61N. I tried it with and without the negative sign and still got it wrong.
 
  • #10
grouchy said:
I tried -178.223 + 107.623 and got -70.61N. I tried it with and without the negative sign and still got it wrong.
That's the work done by friction, in Joules not Newtons. Now find the friction force.
 
  • #11
man..I suck at this physics stuff lol. I forgot that I found the W and not the force. Thx for your help though!
 

What is Kinetic Energy?

Kinetic energy is the energy an object possesses due to its motion. It is a scalar quantity and is dependent on the mass and velocity of the object.

How is Kinetic Energy Calculated?

The formula for calculating kinetic energy is KE = 1/2 * m * v^2, where m is the mass of the object and v is its velocity. The unit for kinetic energy is Joules (J).

What Causes a Change in Kinetic Energy?

A change in kinetic energy is caused by a change in the velocity of an object. If the velocity increases, the kinetic energy will also increase. Conversely, if the velocity decreases, the kinetic energy will also decrease.

What Factors Affect the Change in Kinetic Energy of a Block?

The change in kinetic energy of a block is affected by its mass, velocity, and any external forces acting on it. The mass and velocity of the block determine its initial kinetic energy, while external forces such as friction or applied forces can change its kinetic energy over time.

Can Kinetic Energy Be Converted into Other Forms of Energy?

Yes, kinetic energy can be converted into other forms of energy such as potential energy, heat, or work. This is known as the principle of conservation of energy, which states that energy cannot be created or destroyed, but can only be converted from one form to another.

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