P4.3

Question 1

2. What is the resultant force of an object?

Answer 1

-the sum of all the individual forces acting on it, taking their directions into account

Question 2

2. What effect does the resultant force have on the motion of the object?

Answer 2

• the resultant force decides the motion of the object (accelerate/ decelerate /stay constant)
• the bigger the resultant force, the greater the acceleration
• acceleration means change in velocity, so change in speed OR direction

Question 3

3. What is the relationship between momentum and resultant force?

Answer 3

When a resultant force acts on an object, it causes a change of momentum in the direction of the force

Question 4

4. What is the equation to find momentum?

Answer 4

momentum (kg m/s) = mass (kg) × velocity (m/s)

Question 5

5. What is the relationship between the size of the change of momentum of an object and the size of the resultant force acting on the object and the time for which it acts? (Give equation)

Answer 5

• the size of the change of momentum of an object is proportional to the size of the resultant force acting on the object and to the time for which it acts
  change of momentum (kg m/s) = resultant force (N) × time for which it acts (s)

Question 6

6. How can the horizontal motion of objects be analysed? What is an example of this?

Answer 6

-the horizontal motion of objects (like cars and bicycles) can be analysed in terms of a driving force (produced by the engine or the cyclist), and a counter force (due to friction and air resistance)

Question 7

7. If an object is moving in a straight line, what will happen to the motion of the object if it has these different driving forces?

Answer 7

• greater than the counter force: the vehicle will speed up
• equal to the counter force: the vehicle will move at constant speed in a straight line
• smaller than the counter force: the vehicle will slow down

Question 8

8. In a collision, how can the average force on a human be reduced? (use equation)

Answer 8

-in situations involving a change in momentum (such as a collision), the longer the duration of the impact, the smaller the average force for a given change in momentum
Force=∆momentum/time
-increased time to stop= decreased force
-if a car breaks slowly=forces acting on body are smaller= less likely to be hurt

Question 9

8. Why do you have to increase time when reducing the average force on a human in a collision?

Answer 9

-because you can’t decrease change in momentum as the mass/velocity of the vehicle stays the same

Question 10

9. What are some road safety measures?

Answer 10

• Air bags
• Helmets
• Car seatbelts
• Crumple zones

Question 11

9. How do AIR BAGS help with road safety?

Answer 11

• provides a soft surface so person doesn’t cut/injure themselves on hard surfaces
• air bag gives way on impact= increases time of collision= decreases resultant force= decreases chance of injury

Question 12

9. How do HELMETS help with road safety?

Answer 12

-passing in helmets= increases time of collision= decreases resultant force= decreases chance of injury

Question 13

9. How do CAR SEATBELTS help with road safety?

Answer 13

• prevents person from being thrown about in car and injuring themselves
• seatbelt slightly stretches= increases time of collision= decreases resultant force= decreases chance of injury

Question 14

9. How do CRUMPLE ZONES help with road safety?

Answer 14

-crumple on impact= increases time of collision= decreases resultant force= decreases chance of injury

Question 15

10. How can the vertical motion of objects (falling, or initially thrown upwards) be analysed?

Answer 15

-in terms of the forces acting (gravity, air resistance)

Question 16

11. What happens if the resultant force of an object is at zero?

Answer 16

• its momentum does not change
• if it is stationary, it stays at rest
• if it is already moving, it continues at a constant velocity [a steady speed in a straight line]