# physics-energy

posted by
**becky** on
.

HI well i have two questions

1) a 2.0-m-long pendulum is released from rest when the support string is at an angle of 25 with the vertical. what is the speed of the bob at the bottom of the swing?

2)A 2.0*10^3-kg car starts from rest at the top of a 5.0-m-driveway that is sloped at degree 20 with the horizontal. if an average friction force of 4.0*10^3N impedes that motion, find the speed of the car at the bottom of the driveway.

What is the difference in height the bob swings thru? 2- 2cos25. To the potential energy is mg (2- 2cos25). Set that equal to 1/2 mv^2 and solve for v.

The initial PEnergy is mg*5sin20. THe friction energy is 5*4.0*10^3 joules.

Final KE= initial PE - frictionenergy.