1. A car weighing 15,000 N is speeding down the highway at 90 km/h. What is its

Question

1.   A car weighing 15,000 N is speeding down the highway at 90 km/h. What is its momentum?

2. Two ice skaters stand face to face and "push off" and travel directly away from each other. The boy has a velocity of 5 m/s and he weighs 740 N. The girl weighs 490 N. What is the girl's velocity?

3. A 20,000 kg railroad car is traveling at 3 m/s when it collides and couples with a second, identical car at rest. What is the resulting speed of the combined cars?

4. A soccer player kicks a 1 kg ball with a force of 1000 N. His toe is in contact with the ball for 2 s. What is the impulse?

5. A force of 150 N is required to push a table 5.0 meters across a level floor. How much work was done?

6. If 10,000 J of work was done to raise a 250 kg box, how high was the box raised?

7. What is the velocity of a 1,500 kg car if its kinetic energy is 300 kJ?

8. A 150 kg mass is on a cliff 50 m high. What is its potential energy?

9 How much work is done moving a 2.5 kg book to a shelf 3.0 m high?

10. A 150 pound man runs up a stairway 25 feet above ground level in 10 s. How much work did the man do?

Explanation / Answer

1.mass=15000/9.8 kg

v=90 km/hr=25 m/s

momentum=mass*velocity=(15000/9.8)*25=38265.3 kgm/s

2.By conservation of momentum

initial velocity=final velocity=0=(5*740)+(490*v)=>v=-7.55 m/s (-means direction is opposite to other)

3.By conservation of momentum

new speed=m*3/2m=1.5 m/s

4.impulse=force*time =2000 Ns

5.work =force*displacement=150*5=750 J

6.potential energy=mgh

h=energy/mg=4.08 m

7.kinetic energy=0.5*m*v^2

we get v=20 m/s

8.potential energy=mgh=73500 J

9.work done = change in potential energy=mgh=73.5 J

10.work done=150*25*32.2=120750 pound.feet^2/s^2

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