1. Oct 11, 2007

### malajube

Hi everyone! I am new here and I am asking this question because this year I enrolled in Physics, and my teacher is horrible. On a practice test, we have 3 questions that I just cannot figure out!
Could you all help me? I don't need answers, I just can't understand the formulas, or which ones to use. If you all could just tell me what formulas, I could piece together the rest!

Thank you!
Anna

1) Water flows over a section of Niagra Falls at the rate of 1.2 x 10E6 (to the sixth) kg/s and falls 50.0 m. How much power is generated by the falling water?
a) 9.50 x 10E6 W
b) 5.90 x 10E8 W
c) 1.04 x 10E5 W
d) 6.40 x 10E4 W

2) A 70.0 kg base runner begins his slide into second base while moving at a speed of 4.0 m/s. The coefficent of friction between his clothes and Earth is .70 . He slides so that his speed is 0 just as he reaches the base. How much mechanical energy is lost?
a) -8.4 x 10E2 J
b) -2.3 x 10E3 J
c) -5.6 x 10E2 J
d) -9.5 x 10E4 J

3) (Cont. from question 2) How far does he slide?
a) 1.2 m
b) 5.1 m
c) 8.3 m
d) 3.7 m

2. Oct 11, 2007

### learningphysics

For the first question, deal with energy first before power... in 1s, how much energy is produced... think gravitational potential energy.

For the second question, what is the formula for kinetic energy?

For the third... what is the force of friction... through what distance does the force of friction act to bring the energy of the runner to 0.