KE & work concepts: Work done by a single force on an object during a displaceme
ID: 778117 • Letter: K
Question
KE & work concepts: Work done by a single force on an object during a displacement can be either positive or negative a) Can the total work of all the forces on an object be negative? If so, explain how this can happen. If 9) not, explain why not. b) If the total work can be negative: Can its absolute value be equal to the initial kinetic energy of the object? If so, explain how this can happen. If not, explain why not. Can its absolute value be larger than the initial kinetic energy of the object? If so, explain how this can happen. If not, explain why not. i) ii)Explanation / Answer
(a )In accordance with Work-energy theorem, the change in kinetic energy is equal to work done.
W = 1/2 mvf^2 - 1/2 mvi^2
An increase in the kinetic energy is caused by an equal amount of positive work done on the body by the resultant force. In the same way, a decrease in kinetic energy is caused by an equal amount of negative work done by the resultant force.
Example: Friction opposes motion and as such does negative work
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(b)
(i) Expression for work-energy theorem;
W = 1/2 mvf^2 - 1/2 mvi^2
In the case of final speed of object is zero, the absolute value of neagtive work doen on the body is equal to
initial kinetic energy.
(ii) In the case of negative work, the final kinetic energy must be less than initial kinetic energy. ( velocity decreases).
Hence, the the abosute value of work done not equal to initial kinetic energy.
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