Kinetic Energy of some mass

In summary: If you don't, it's okay.In summary, the conversation discusses the calculation of kinetic energy for a block sliding along a loop-the-loop track. The equation used is K1 + PE1 = K2 + PE2, where K represents kinetic energy, PE represents potential energy, and the subscripts 1 and 2 represent the initial and final points, respectively. The conversation also touches on the importance of choosing a fixed origin point for measurements.
  • #1
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[SOLVED] Kinetic Energy

A small block of mass m = 1.5 kg slides, without friction, along the loop-the-loop track shown. the block starts from the point P at rest a distance h = 55.0 m above the bottom of the loop of radius R = 19.0 m. What is the kinetic energy of the mass at the point A on the loop?
prob17a.gif


So I use conservation of energy K1 + PE1 = K2 + PE2 or .5mv^2(1) + mgR(1) = .5mv^2(2) + mgR(2)

At point A there's 0 KE.

Is this right? Do I just plug numbers in?
 
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  • #2
.5mv^2(1) + mgR(1) = .5mv^2(2) + mgR(2)

This equation seems to be correct, but how did you get KE= zero ??
 
  • #3
assumption...

is it not zero?
 
  • #4
Noo. At point P there is 0 KE. At point A there is. Tell me what are R(1) and R(2)? Then you can plug numbers in.
 
  • #5
R(1) and R(2) is the radius - 19m
 
  • #6
Nope. What you are calling mgR should be written mgh where h is the vertical displacement from some fixed position of your choice. h is 55m at P. What is it at A?
 
  • #7
PE = 0 at A
 
  • #8
am08 said:
PE = 0 at A

You can make that choice. Then what is PE at P?
 
  • #9
Wouldn't it be mgh
 
  • #10
Let's keep this simple. PE=mgh. They gave you h=55m at P. So PE at P is mg(55m). What's h at A? Then what's PE at A?
 
  • #11
17 m

Got it dick... thanks for sticking with me and helping me out with this problem
 
  • #12
Nope. 38m. You keep changing origins on me! Pick a zero point and stick with it. If we say h=55m then we are measuring everything from the horizontal line in your picture. You could also measure everything from any other point but that's too confusing. Let's just stick with this one.
 
  • #13
I gather you got the right answer. Yes, 55m-38m=17m. So mg(17m)=(1/2)mv^2. If you understand it, that's great.
 

What is kinetic energy?

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

How is kinetic energy calculated?

Kinetic energy (KE) is calculated using the formula KE = 1/2 * mass * velocity^2. The unit for kinetic energy is Joules (J).

What factors affect the kinetic energy of an object?

The kinetic energy of an object is affected by its mass and velocity. The greater the mass and velocity of an object, the greater its kinetic energy will be.

What is the difference between potential energy and kinetic energy?

Potential energy is the energy an object possesses due to its position or state, while kinetic energy is the energy an object possesses due to its motion. Both types of energy are measured in Joules (J).

How is kinetic energy related to work?

Kinetic energy is directly related to the work done on an object. The work done on an object is equal to the change in its kinetic energy.

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