P5

Question 1

state 3 uses of artificial satellites

Answer 1

• satellite navigation
• producing images of Earth
• weather predictions
• military uses e.g. spy satellites
• scientific research

Question 2

describe how the force of attraction varies with with distance

Answer 2

inverse square law - for example, if the distance from earth is trebled, then the force of attraction will be 1/9 of the original

Question 3

describe the orbit and speed of a comet

Answer 3

• highly elliptical orbit
• comet has higher speed when closer to the sun, due to there being a stronger gravitational attraction
• comet has a lower speed when further away from the sun, as there is a weaker gravitational attraction

Question 4

what is the orbital time period of a satellite?

Answer 4

how long it takes a satellite to orbit once around the Earth

Question 5

state the 2 types of satellite orbits

Answer 5

• geostationary

- low polar

Question 6

state 2 uses of satellites in low polar orbits

Answer 6

• weather forecasting

- producing images of Earth

Question 7

state 2 uses of satellites in geostationary orbits

Answer 7

• telecommunications (TV)

- GPS (for sat nav)

Question 8

describe the orbits of low polar and geostationary satellites

Answer 8

• low polar - closer to Earth so faster, so orbital time period of about 2 hours
• geostationary - fixed position position above Earth’s surface, further away from Earth, orbital time period of 24 hours, orbits above the Equator

Question 9

explain how artificial satellites continually accelerate towards the Earth

Answer 9

• the centripetal force (in this case gravity) always acts towards Earth and at a right angle to the satellite’s motion
• satellites continually change direction, so they continually change velocity, and therefore continually accelerate towards Earth

Question 10

what is the optimum angle?

Answer 10

45’ - the launch angle which provides the greatest range

Question 11

state the 2 types of forces acting on an object

Answer 11

• a pair of contact forces (e.g. push/pull)

- a pair of forces due to gravitational attraction

Question 12

what is the backwards force called when you fire a gun?

Answer 12

recoil

Question 13

explain how a rocket moves

Answer 13

1. rocket fuel is burnt at very high temperatures, releasing high energy particles which move very fast
2. these particles collide with the walls of the combustion chamber, causing them to change momentum
3. this high collision rate provides a high rate of momentum change
4. the high rate of momentum change produces a large force, causing the rocket to accelerate upwards

Question 14

explain the law of conservation of momentum

Answer 14

total momentum before = total momentum after