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Wed May 04, 2011 12:41 pm
Funkymomo says...



These are word problems I'm having trouble with, you don't have to do all of them, one or two would help! You don't even have to do the math,just tell me how. :(

1. Dr. Octopus breaks the controls of a train, sending it speeding down the tracks at 35.76 m/s. Spider-Man jumps in front of the train and shoots his webs to the adjacent buildings to make a sling of himself. Each car of the train is 21,500 kg, and it has 6 cars. Assume there are 20 passengers, each weighing 67.5 kg, in each car. Find the force Spider-Man has to exert to stop the train if it takes him 46 seconds.

3. Find the distance the train traveled from the time Dr. Octopus broke the controls to the time Spider-Man stopped it.

4. Spider-Man loses control of his web-shooters for 4 seconds while swinging between buildings. Find how far he falls before he regains control.


6. Spider-Man started his fall from the roof of a 100 m high building. Find out how long it would have taken him to crash to the ground if he had not regained control of his web-shooters.

7. Spider-Man hears Mary Jane cry for help from inside a room with a large box blocking a door. To let MJ out, Spider-Man lifts the box as high as his head. The mass of the box is 200 kg, and Spider-Man is 2 m tall. How much work does Spider-Man do to rescue MJ?



10. Spider-Man is chasing the Green Goblin through the streets in a car chase. The Green Goblin stops his car to let an adorable kitten cross the road (see, he’s not totally evil!). Spider-Man isn’t used to driving, since he usually travels by web. He is driving his car at a velocity of 15 m/s when he hits the Green Goblin’s car (don’t worry, the kitten has safely made it to the other side of the road by now). Spider-Man’s car is stopped by the collision and the Green Goblin’s car moves away at a velocity of 12 m/s. The total mass of Spider-Man plus his car is 968 kg. If the Green Goblin’s car has a mass of 1070 kg, what is the mass of the Green Goblin in kg? Assume that there is no loss of momentum due to friction. (Hint: remember the law of conservation of momentum.)
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Wed May 04, 2011 3:26 pm
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Kyllorac says...



For 1, you're dealing with impulse, so you'll need the total mass of the train and passengers, their velocity, and the time needed to stop the train to find it's total force on Spiderman's web. Since all forces exert equal and opposite forces on one another, the force Spiderman's web exerts on the train will be the same, but in the opposite direction.

For 3, you know the time it took for the train to stop, its initial velocity, and by calculating the force you've learned the acceleration, so you can use the kinematics equation relating position to velocity and acceleration as a function of time.

For 4 and 6, the acceleration downwards will be due to gravity. You can again use the kinematics equation for position, and set the initial velocity and position to 0 since we're assuming he wasn't falling before the four seconds, and he definitely wasn't falling through the roof.

For 7, work is force times distance. How much force is exerted on the box when it's at rest, and how far is it being moved?

For 10, momentum is mass times velocity. The final total momentum has to be equal to the total initial momentum. Because the Green Goblin is initially at rest, his momentum is 0. After the collision, Spiderman's momentum is 0 because he's come to a complete stop. As a result, Spiderman's inital momentum is the same as the Green Goblin's final momentum. Since you've been given the Green Goblin's final velocity and the mass of his car, you'll be able to calculate how much mass the Green Goblin and his car have, and then how much mass the Green Goblin has.
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Thu May 05, 2011 12:11 am
WritersUnleashed says...



Though im no good at physics, Im quite entertained by the spiderman stuff....