Forces - Paper 2

Question 1

Two cars are travelling along a road. The car in front is travelling at 20m/s and has a mass of 800kg. The car behind is travelling at 30m/s and has a mass of 1000kg. The second car collides with the back of the first car and they lock together. Calculate the combined speed of the two cars after the collision.

Answer 1

Total momentum before collision = 46 000 kg m/sTotal momentum after collision = 46 000 kg m/sMomentum = mvv=momentum/mv=46 000/1800v=25.55 m/s

Question 2

A locomotive of mass 20000kg travelling at 28 m/s heads towards a carriage of mass 8000kg heading in the other direction at 15 m/s. If the carriage rebounds from the collision at a speed of 10m/s then what speed will be the velocity of the locomotive after the collision?

Answer 2

Total momentum before = m1v1 + m2v2
Total momentum before = 440000kgms-1
Total momentum after = 440000kgms-1.
m1v3 + m2v4 = 440000 v3 = 360000/20000 = 18ms-1

Question 3

What is the similarity and difference between scalars and vectors.

Answer 3

Similarity - they both have magniture

Difference - A vector also has direction

Question 4

Is density a scalar or vector?

Answer 4

scalar

Question 5

Is energy a scalar or vector?

Answer 5

scalar

Question 6

Is force a scalar or vector?

Answer 6

vector

Question 7

Is momentum scalar or vector?

Answer 7

vector

Question 8

Is speed a scalar or vector?

Answer 8

scalar

Question 9

Is velocity a scalar or vector?

Answer 9

vector

Question 10

Is distance a scalar or vector?

Answer 10

scalar

Question 11

Is mass a scalar or vector?

Answer 11

scalar

Question 12

Is acceleration a scalar or vector?

Answer 12

vector

Question 13

Is time a scalar or vector?

Answer 13

scalar - e.g. 60 seconds

Question 14

Is displacement a scalar or vector?

Answer 14

vector

Question 15

What is the equation for momentum?

Answer 15

momentum = mass x velocity

Question 16

A car of mass 400kg is moving at a speed of 25ms-1. Calculate its momentum.

Answer 16

10000 Kg m/s

Question 17

If a vehicle has a momentum of 15000 kgms-1 and a speed of 30ms-1, what is its mass?

Answer 17

500 kg

Question 18

If a vehicle has a momentum of 20000 kgms-1 and a mass of 1500 kg, at what speed is it travelling?

Answer 18

p = 13.33ms-1

Question 19

State the equation linking force, change in momentum and time

Answer 19

force = change in momentum / time taken

force = mv - mu /t

or

change in momentum = force x time taken

Question 20

Name 3 safety features that reduce the risk of injury in a car crash.

Answer 20

1. Seat belts
2. Airbags
3. Crumple Zones

Question 21

Explain how seat belts can reduce injuries to passengers during a crash.

Answer 21

Change in momentum= time taken x force

1. The seat belt increases the time of impact which reduces the forces on the body as momentum changes to zero.
2. The seat belt stretches which increases the area over which the force acts reducing the pressure on the body.

Question 22

Explain how airbags can reduce injuries to passengers during a crash.

Answer 22

change in momentum=time x force

1. Air bags increase the time taken for the head’s momentum to reach zero, so reduce the forces on it.
2. They act a soft cushion and prevent cuts.

Question 24

Explain how crumple zones can reduce injuries to passengers during a crash.

Answer 24

change in momentum = time x force

1. Crumple Zones increase the time it takes for the car to stop. Increasing the time reduces the forces impacting the car and the forces on the passengers inside the car.

Question 25

What happens to the momentum of a car during a crash?

Answer 25

It reduces to zero in a very short amount of time and therefore exerts a high amount of force on the car.

Question 26

Why is a full body harness used in a racing car instead of a seatbelt?

Answer 26

1. Race cars are faster than ordinary cars and therefore the forces on the body would be greater in a crash.
2. The seat belts have a greater surface area and this reduces the pressure on the body.

Question 27

If a vehicle has a momentum of 20000 kg m/s and a mass of 1500 kg, at what speed is it travelling?

Answer 27

p = mvv = p/mv = 20000/1500p = 13.33 m/s

Question 28

If a vehicle has a momentum of 16000 kg m/s and a speed of 25m/s, what is its mass?

Answer 28

p = mvm = p/vm = 16000/25m = 640kg

Question 29

A car of mass 500kg is moving at a speed of 30 m/s. Calculate its momentum.

Answer 29

p = mvp = 500 x 30p = 15000 kgms-1

Question 30

Describe what is happening in each of the pictures?

Answer 30

picture 1 - downward force (weight) is greater than upward force (air resistance)- sky diver is accelerating

picture 2 - air resistance is increasing so sky diver is acceelerating more slowly

picture 3 - sky diver has reached terminal velocity

Question 32

When a force acts at an angle to an object it produces a turning effect. What is this called?

Answer 32

A moment

The moment of a force about a fixed point or axis is the turning effect of the force about that point and is measured by the product of the force and the perpendicular distance from the point to the line of action of the force.

Question 33

What is the equation for moments?

Answer 33

moment = force x distance of force from pivot

or

moment = F x d

Moment in Nm
Force in N
Distance in M

Question 34

A beam is laid across a pivot. 200 N is applied to one end of the beam at a distance of 2.5m from the pivot:

Answer 34

moment = 200 x 2.5 = 500 Nm

Question 35

A beam is laid across a pivot. 400N is applied to one end of the beam at a distance of 3.5m from the pivot.

Answer 35

moment = 400 x 3.5 = 1400 Nm

Question 36

We can use this equation to calculate the orbital speed:

Question 37

How fast would a satellite move if it was orbiting at a height of 100km and each orbit took 1.44 hours?