Answer to Question #114453 in Mechanics | Relativity for Jason Grace

Question #114453

A 48.0 kg in-line skater begins with a speed of 2.2 m/s. Friction also does (-150) J of work on her. Assume that se did not push on the ground any more. If her final speed is 5.9 m/s,

a) determine the change (final-initial) in her gravitational potential energy.

b) By how much, and in which direction (up or down), has her weight changed?

Please answer using grade 11 Conservation of Energy and Momentum .

Expert's answer

As per the given question,

mass of the line skater "(m)=48 kg"

speed of the line skater "(u)=2.2 m\/sec"

work done by friction force "(w)=-150J"

her final speed "(v)=5.0m\/sec"

a) Applying the conservation of energy,

Initial potential energy "(U_1)=\\dfrac{mu^2}{2}"

Final energy "(U_2)=\\dfrac{mv^2}{2}-150"

so, change in PE"=\n\\dfrac{48\\times 5.9^2}{2}-\\dfrac{48\\times 2.2^2}{2}-150=(835.44-232.32-150 )J=453.12J"

b)Weight of the skater is working downwards, because as she is moving downwards, her speed is getting increase, it means it is getting accelerate towards the ground.

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