7. A 10kg block is at rest on the floor... 8. A 7.0kg bowling ball is moving at

Question

7. A 10kg block is at rest on the floor... 8. A 7.0kg bowling ball is moving at 3... 9. A 5 N block rests on an incline... 10. A 2 kg ball is held motionless... 11. If the surface is frictionless 12. If there is friction...
So I know the answers to all the questions(they're circled) but for some if them I'm confused on how that answer was found! Please show all work with explanation to all 6 questions for all points! Thanks! 7. A 10 kg block is at rest on the floor, and then a force of 30 N pushes in the block horizontal. If the coefficient of static friction between the block and the floor is Mu = 0.33 and the coefficient of kinetic friction between the block and the floor is Mu = 0.20, what is the acceleration of the block , if it slides ?

Explanation / Answer

1.frictional force= usmg=10*9.81*0.33=32.37N

it is greater than 30 ,it dont slide

2.1/2mbvb^2=1/2mpvp^2

vp=sqrt(mb/mp)vb=sqrt(7000/2.5)*3=158.74m/s=159m/s

9. a=gsintheta-ugcosthtea=0

so v=1m/s

10.work done =-1/2kx^2=-1/2*882*0.2^2=-17.64J

11.1/2mv^2=1/2kx^2

x=sqrt(m/k)v=2.34m

12.work done by friction=-(1/2mv^2-1/2kx^2)=-218J

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