# physics finding kinetic energy

#### zelda1850

Joined Jan 3, 2010
18
a 20 kilogram block is placed at the top of a 10 meter long inclined plane. the block starts from rest and slides without friction down the length of the incline

determines the kinetic energy of the block just as it reaches the bottom of the incline

mass = 20 kg
distance = 10 m
height = 10 m

the forumla is ke = 1/2 mv square

but i dont have velocity what is the other forumla i can use to solve this problem?

#### mik3

Joined Feb 4, 2008
4,843
Find the slope of the inclined plane and then the analyse the weight of the block into its x-y components The x component is should be in parallel with the inclined plane. Use the x component to find the final velocity of the block and thus its kinetic energy.

Joined Jul 7, 2009
1,583
Before worrying about what formulas to use, go back and read your textbook to understand the principles involved first. Read about conservation of energy, kinetic energy, and potential energy. You should then be able to make a statement about what principles are involved here. Once those principles are clear in your mind, the solution is pretty obvious and involves only a couple of simple formulas.

Because there's no friction, the mechanical energies are conserved. If you've studied potential energy, consider the change in potential energy of the block and how it might be related to the kinetic energy of the block.

#### Papabravo

Joined Feb 24, 2006
16,484
There appears to be a misprint. The inclined plan cannot be 10 m long (the hypotenuse) and 10 m high (one of the sides). That would make it a vertical wall and not an inclined plane.

#### mik3

Joined Feb 4, 2008
4,843
There appears to be a misprint. The inclined plan cannot be 10 m long (the hypotenuse) and 10 m high (one of the sides). That would make it a vertical wall and not an inclined plane.
Maybe it does not mean the length of the inclined level itself but its base length.

#### Papabravo

Joined Feb 24, 2006
16,484
Maybe it does not mean the length of the inclined level itself but its base length.
Plausible. The OP needs to clarify the original question.

#### Heavydoody

Joined Jul 31, 2009
140
Does the length of the ramp matter in this situation?

#### mik3

Joined Feb 4, 2008
4,843
Does the length of the ramp matter in this situation?
Yes, that is a good point. The length does not really matters, it is the height that matters as to calculate the potential energy of the block. Then the kinetic energy at the end of the incline equals the potential energy assuming no friction.

Good point Heavydoody.

#### Heavydoody

Joined Jul 31, 2009
140
One of the benefits of frictionless ramps and drag-free objects...unfortunately, they seem to be somewhat rare...well, except in physics textbooks

#### zelda1850

Joined Jan 3, 2010
18
oppps i forgot to add that there was a picture with the question showing that the height was 10 meters

#### mik3

Joined Feb 4, 2008
4,843
Did you understand how to solve it?

#### zelda1850

Joined Jan 3, 2010
18
nope is their a formula?

#### Heavydoody

Joined Jul 31, 2009
140
In an isolated system with only conservative forces,
ΔK+ΔU=0.