Physics 7 (Winter 08) – Homework #4

Due: 2/5

 

1.      Satellites are kept in orbit because of gravity, and apples fall to Earth because of gravity. Why don’t satellites fall and why are apples not in orbit?

2.      Imagine that John carries a charged sphere and decides to run back and forth in front of Mary. Using appropriate measuring devices, she finds

    1. That the charge on the sphere steadily increases
    2. That there are no electric or magnetic effects near her
    3. That the charge leaps from the sphere to her
    4. That the charge on the sphere steadily decreases
    5. That a small magnetic field is generated

3.      A spacecraft in outer space moves forward because

    1. Of the reaction it experiences by expelling the gases from its rockets
    2. Of the fire from its rockets
    3. It is fiery and so it moves away from Earth
    4. There is no friction in space
    5. There is no gravity in space

4.      The Moon pulls objects towards it and the Earth does the same. An object is placed between the Earth and the Moon, then

    1. There is a point where the pulls form Earth and Moon are balanced and the object stays put
    2. It will always fall towards the Earth, because it is more massive
    3. It will always start orbiting the Earth
    4. It will float in place wherever it is since there is no gravity in space
    5. It will always start orbiting the Moon

5.      According to Newton all bodies attract each other gravitationally, this force

    1. Is identical forces in all cases and circumstances
    2. Is larger the more massive the bodies are and the closer they are
    3. Increases with distance
    4. Decreases with distance between the bodies but does not depend on the masses
    5. Increases with the masses but does not depend on the distance between the bodies

6.      The speed of light is very large but not infinite. This implies that when we see some distant event

    1. The event happened a short time before we see it
    2. The event happens at precisely the same time we see it
    3. The event will happen a short time after we see it
    4. The even could happen before or after we see it depending on our speed
    5. The event could happen before or after we see it depending on our acceleration

7.      If one breaks a magnet (S denotes the “south” pole and N the “north” pole)

    1. If the break is close to the S pole one gets a piece with N and S poles and another piece with only a S pole
    2. One gets a piece with a S pole and another with an N pole
    3. Both pieces have S and N poles wherever the break occurs
    4. Both pieces have S and N poles only if the break is precisely in the middle
    5. If the break is close to the N pole one gets a piece with S and N poles, and another with only an N pole

8.      When we bounce a ball off a wall the wall does not move, this is because

    1. Newton’s 3rd law fails
    2. The force is small and its mass is enormous
    3. The force on the wall is zero
    4. Of the friction between wall and ball
    5. Of the air resistance experienced by the ball as it bounces.

9.      As a magnet is moved through a coil of wire a current is generated. Now, if one keeps the magnet steady and moves the coil

    1. Nothing happens
    2. The strength of the magnet increases
    3. A current is also induced
    4. The strength of the magnet decreases
    5. The charges form the coil are transferred to the magnet

10.  Maxwell equations predict that light moves at 300,000 km/s with respect to

    1. The frame of reference in which the observer is at rest
    2. The frame of reference in which the light source is at rest
    3. The frame of reference of the Earth
    4. Any observer in any reference frame
    5. The ether