## alexyn 3 years ago A child pulls a 15-kg sled containing a 5.0-kg dog along a straight path on a horizontal surface. He exerts a force of 55 N on the sled at an angle of 20° above the horizontal, as shown in the figure above. The coefficient of friction between the sled and the surface is 0.22. a. Calculate the normal force of the surface on the system. b. Calculate the acceleration of the system. c. Calculate the work done by the child's pulling force as the system moves a distance of 7.0 m

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1. alexyn

d. At some later time, the dog rolls off the side of the sled. The child continues to pull with the same force. On the axes below, sketch a graph of speed, v, versus time, t, for the sled. Include both the sled's travel with and without the dog on the sled. Clearly indicate with the symbol tr the time at which the dog rolls off.

2. ksaimouli

can u do me a favor can u draw the diagram

3. alexyn

sure

4. ksaimouli

what part u r struck

5. ksaimouli

ok so (a) FN=mg-Fsin 20

6. alexyn

Part D

7. ksaimouli

i am sorry i am weak at graphs :-(

8. ksaimouli

@ivanmlerner can u help her please

9. alexyn

thanks for trying though

10. ivanmlerner

It is only in part d that you need help?

11. alexyn

12. ivanmlerner

Ok, you know the aceleration before the dog jumps out, so you can draw the graph of v until that moment by using the aceleration as the slope of the line because it is the rate of change of the velocity. Do you understand it so far?

13. alexyn

Yes.

14. alexyn

Im unsure about the acceleration. I got 0.07 m/s. Is that right?

15. ivanmlerner

Just to be sure, what number are you considering for g?

16. ivanmlerner

10 or 9.8?

17. ivanmlerner

I'll be back in a few minutes but I got 0.43 with 9.8

18. alexyn

-10

19. alexyn

ok. I got 1.64 m/s now

20. furnessj

So, I had a go at this, I get a) 177.4N b) 0.63 m/s/s c) 362J As for d) - the question says to sketch, so you do not need values. You just need to realise that with less mass but the same force, the acceleration will be greater, so the slope must get steeper: |dw:1352244868726:dw|

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