Need help with physics HW

7. A 1.80 kg box is held in place at the top of a 30-degree incline and then released. It slides down the incline which is 1.20 m in length. If the coefficient of kinetic friction between the box and incline is 0.20, What is the velocity of the box when it reaches the bottom of the incline? (A] 2.4 m/s (B] 3.4 m/s (C) 6.3 m/s (D] 8.2 m/s 8. A 2.0 kg box is sliding down a ramp with a constant velocity of 5 m/s. The initial height of the block is 3m and the coefficient of kinetic friction between the box and incline is 0.34. How much work is done by friction as the block slides all the way down the ramp? (A) 20 J [B] - 20 J (C) 53.5 J (D] -53.5 J 9. A woman runs up a flight of stairs. The gain in her gravitational potential energy is 6500 J. a) If the woman has a mass of 56 kg, how high is the flight of stairs? b) If she runs up the stairs at half the speed, what is her gain in gravitational potential energy? c) How much potential and kinetic energy does she have when she is half-way up the stairs? d) How much work does she do to get to the top of the stairs? 10. How much work does a supermarket checkout attendant do on a can of soup he pushes 0.600 m horizontally with a force of 5.00 N? I I. I low much work is done on a 1500-kg elevator car by its cable to lift it 40.0 m at constant speed, assuming friction averages 100 N