Homework SourseA 532kg skateboarder starts out with a speed of 168 ms He do
A 53.2-kg skateboarder starts out with a speed of 1.68 m/s. He does 115 J of work on himself by pushing with his feet against the ground. In addition, friction does -220 J of work on him. In both cases, the forces doing the work are non-conservative. The final speed of the skateboarder is 8.77 m/s. (a) Calculate the change (PEf - PE0) in the gravitational potential energy. (b) How much has the vertical height of the skater changed? Give the absolute value.
Solution
Work done by himself=115
work done by friction=-220 J
net work done=115-220=-105
Wnc = (KEf - KEi) + (PEf - PEi).
where Wnc is work done by non conservative force
KEf-KEi=0.5*m*(8.77^2-1.68^2)=1970.8 J
PEf-PE0=Wnc-1970.8=-2075.8 J
PEf-PE0=mg*change in height
2075.8/(53.2*9.8)=3.98 m
change in height=3.98 m
| Wnc = (KEf - KEi) + (PEf - PEi). KEf-KEi=0.5*m*(8.77^2-1.68^2)=1970.8 J PEf-PE0=Wnc-1970.8=-2075.8 J PEf-PE0=mg*change in height 2075.8/(53.2*9.8)=3.98 m change in height=3.98 m |
