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

Question

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 .

Answer 1

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$= \dfrac{48\times 5.9^2}{2}-\dfrac{48\times 2.2^2}{2}-150=(835.44-232.32-150 )J=453.12J$

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.