Conceptual Physics

Variables

What is the strategy?

1. Calculate the change in kinetic energy of the sled, using the sled’s mass and its initial and final speeds.


2. Use the work-kinetic energy theorem and the definition of work to find the force exerted on the sled.

Physics principles and equations

The definition of work, applied when the force is in the direction of the displacement

W = Fǻx

The definition of kinetic energy

KE =½mv^2

The work-kinetic energy theorem

W =ǻKE

Step-by-step solution

Start by calculating the change in kinetic energy of the sled.

Use the work-kinetic energy theorem to find the work done on the sled. Then, use the definition of work to determine how much force was
exerted on the sled.

mass of sled m = 235 kg

displacement ǻx= 50.0 m

sled’s initial speed vi = 0 m/s

sled’s final speed vf = 10.0 m/s

work W

force F

Step Reason

1. ǻKE = KEf – KEi definition of change in kinetic energy

2. ǻKE = ½mvf^2 – ½mvi^2 definition of kinetic energy

3. ǻKE = ½m(vf^2 – vi^2 ) factor

4. enter values

5. ǻKE = 11,800 J solve

Step Reason

6. W = ǻKE work-kinetic energy theorem

7. W = (F cos ș)ǻx definition of work

8. (F cos ș)ǻx = ǻKE set two work equations equal

9. F cos ș = ǻKE/ǻx rearrange

10.F = ǻKE/ǻx force in direction of displacement

11.F = 11,800 J/50.0 m enter values

12.F = 236 N solve

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