A ball is held at a height H above a floor. It is then released and falls to the

Question

A ball is held at a height H above a floor. It is then released and falls to the floor. If air resistance can be ignored, which of the five graphs below correctly gives the mechanical energy E of the Earth-ball system as a function of the altitude y of the ball? I II III IV V A 2.2-kg block starts from rest on a rough inclined plane that makes an angle of 25 degree with the horizontal. The coefficient of kinetic friction is 0.25. As the block goes 2 0 m down the plane, the mechanical energy of the Earth-block system changes by: 0 -98 J 9 8 J -18 J 18 J

Explanation / Answer

9.

mechanical energy of the system will remain constant w.r.t H, due to the enegry conservation theroam

Correct option is E.

10.

mass of block = 2.2 kg

weight of block parallel to incline will be

W = m*g*sin A

Wp = 2.2*9.81*sin 25 deg = 9.12 N

weight of block normal to incline

Wn = 2.2*9.81*cos 25 deg = 19.55 N

frictional force will be

Ff = uk*Wn

Ff = 0.25*19.55 = 4.89 N

Change in mechanical energy will be equals to the frictional work.

Wf = - Ff*d

Wf = -4.89*2 = -9.78 J

correct option is B.

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