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Work
| Energy: |
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| Example: |
If you push an object through a certain distance (d), using a force (F), you can calculate the amount of work done in moving the object (mass m) a distance (d)....................... |
WORK = Force X Parallel Distance
W = (F )(d)(cos q)
Where F is the Force doing the "pushing" and d is the distance the object moves. The distance and the force must be in the same direction.
In this equation, Force is measured in [N], and distance is measured in [m].
| WORK = Energy | Measured in Joules 1 Joule = 1 Newton-meter 1 J = 1Nm
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Example 1: |
An old lady pushes a cart with a force of 100 N, Through 50 m. How much energy is she using up, and how much work is she doing on the cart? |
Solution:
Given: F = 100 N
d = 50
m
Find: W
W = F x d
= 100 N x 50 m = 5000 J
\The old lady uses up 5000 N of Energy in pushing the cart. At the same time, the work she is doing on the cart is also 5000N since Work = Energy.
If Work = Force x distance then, Energy = Force x distance.
Work done in LIFTING objects.
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The mass is being lifted from h1 to h2 against gravity. The change in height (Dh) is h2 - h1. The same equation for calculating work done in lifting can be applied. W = F x d = Fg x h = m x g x h.
Therefore, the work done in lifting an object against gravity can be calculated using the equation
W
= m x g x h
This type of work is representative of the amount energy used in lifting the object. Because the object is being lifted against gravity, this energy is known as the Gravitational Potential Energy (Ep). It is a potential energy because, once lifted to a height above ground, the object has the potential of producing energy if released from that height.
Ep = m x g x Dh
Example 2:
What is the work done by an elevator on 5 people (800 Kg) inside the elevator, if they all get off on the 4th. floor (12 m above the ground)?
Solution:
Given:
m = 800 Kg, g = 9.8 N/Kg, h = 12 m
Find: W
W = m x g x h
= 800 Kg x 9.8 N/Kg x 12 m
= 94080 Nm
= 94 080 J
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(Next Topic) Potential & Kinetic Energy
