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Homework Help: Study Guide Problems

  1. Dec 30, 2011 #1
    1. The problem statement, all variables and given/known data

    I have these questions from a study guide in physics. I don't understand how to answer any of these and am completely lost in physics. I'm looking for any help I could get in explaining how to do these problems. I'm new to this site and not sure if this is posted right or anything but would someone please be willing to help me with solving any of these?

    1. Consider two identical cars (1400 Kg) moving along a road at a speed of 20 m/s. The blue car is stopped by the car’s brakes in 25 m while the green car is stopped by a concrete barrier in 1.2 m. The drivers of the two cars are the same mass (70 kg). The driver of the blue car is stopped by the seat belt in the same motion as the car. The driver of the green car is stopped by a seat belt/air bag in 0.150 sec.

    Compare the change in momentum of each car.
    Compare the impulse received in stopping for each driver.
    Calculate the average force exerted on each driver in stopping.
    Explain whether a larger mass driver in the green car would experience a larger stopping force relative to their weight if they are stopped in the same time. (i.e. if they had twice the mass would they feel twice the force, or less, or more?)

    2. You throw a tennis ball straight up into the air at the same time your cousin throws one straight down from the same height.
    To answer the following questions, choose your own values for the initial height and initial speeds of the thrown balls. Your answers must be supported by calculation or physical law. (hint: the lower the initial height the more precise your calculations need to be)
    Which ball, if either,
    lands on the ground first?
    has the greater acceleration?
    lands with a higher speed?
    travels the farther distance?
    has the greater final displacement?

    3. The International Space Station (ISS) just celebrated its 10th anniversary of human habitation. During that time it has been orbiting the earth at an altitude of 350 Km.
    If the radius of the earth is 6,370 Km, what is the period of orbit for the ISS?
    Does the orbiting speed of the ISS depend on its mass?
    Suppose the ISS is in a stable orbit when the space shuttle brings in a new component for attachment. This increases the mass of the ISS. Do the astronauts have to adjust the speed of the shuttle to maintain the same orbit? (hint: momentum is always a factor in our universe) Explain your reason for your answer.
    If the ISS were to be moved to a geosynchronous orbit (always staying above the same point on the earth), What would the new altitude of the ISS have to be?

    4. Consider the following two cases:
    Case A: A glob of mud is thrown against a wall. It hits the wall with a speed of V and stops in time T.
    Case B: A ball is thrown against a wall. It hits the wall with speed V and comes away from the wall a time T later at a speed of 0.5V.
    (In both cases V and T have the same value and the masses of the mud and the ball are the same.)

    Explain which case you think involves a greater total force on the object(mud or ball) and support your answer.

    5. Pick a game you like to play which requires some physical motion of some kind. Any game - card game, board game, athletic game, party game, any game. For your chosen game, explain where Newton's three laws are applied in playing the game. Your explanation should be detailed enough so a person not familiar with the game (even a common one) would be able to understand your statements.

    6. A golf club contacts a golf ball for 0.15 s at an angle to the horizontal and the ball subsequently strikes the ground a distance down the fairway. You choose an initial speed (between 25 m/s and 35 m/s) and the angle of projection (Between 15o and 22o) to calculate
    the time between the ball leaving the club and when it first touches the ground,
    the range of the ball down the fairway , and
    the average force exerted by the club on the ball.
    (assume the fairway is level horizontally. Mass of a golf ball is 0.046 kg)

    7. You are riding in a car (moving at a constant velocity) and see an open manhole in the road ahead. You take a cantaloupe out of the grocery bag and hold it out the window of the car. Doing a quick calculation you know how far (in meters) ahead of the hole you have to drop the cantaloupe for it to land in the open hole without bouncing on the road. Choose your own speed of the car (between 10 m/s and 20 m/s) and initial height of the cantaloupe (between 1.0 m and 2.0 m) and show the calculations you used and the resulting lead distance for successfully dropping the fruit.
  2. jcsd
  3. Dec 30, 2011 #2
    One of the rules here is that you show us what you've tried and where you're stuck, basically show that you've given it a try and we'll give you hints and tips as you go.
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