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February 28, 2015

February 28, 2015

Posted by **Yarielis** on Thursday, March 20, 2014 at 5:16pm.

- physics -
**Elena**, Thursday, March 20, 2014 at 6:30pm1. PE=KE

PE=mgh=mg•s•sinα

KE=mv²/2

mg•s•sinα=mv²/2

v=sqrt(2g•s•sinα) =

=sqrt(2•9.8•1.8•sin22°)=3.64 m/s

v=at => a=v/t

s=at²/2= vt²/2t=vt/2

t=2s/v=2•1.8/3.64 =0.99 s

2.

t₁=2t=0.99•2=1.98 s

v₁=2s/t₁=2•1.8/1.98= 1.82 m/s

PE=KE+W(fr)

W(fr) = F(fr)s=μ•mg•cosα•s

mg•s•sinα= mv₁²/2 + μ•mg•cosα•s

μ=(g•s•sinα- v₁²/2)/ g•cosα•s=

=tanα - (v₁²/2g•cosα•s)=

=tan22°-(1.82²/2•9.8•cos22°•1.8)=0.3

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