P10 Forces and Motion

Question 1

What is the equation for the resultant force?

Answer 1

Fres=massxacceleration

Question 2

What does newton’s second law say?

Answer 2

acceleration is proportional to the resultant force and inversely proportional to the mass

Question 3

What is inertia?

Answer 3

The tendency of an object to stay at rest or at uniform velocity if no other forces are acting upon it.

Question 4

What is inertial mass and its formula?

Answer 4

The difficulty of changing an objects velocity
force/acceleration

Question 5

If the velocity of an object changes, what must be happening?

Answer 5

The resultant force is acting upon it in the same direction as the acceleration

Question 6

The difference between mass and weight.

Answer 6

Weight is your mass x gravitational field strength and is the force acting upon a object measured in Newtons
Mass is the quantity of matter in an object measured in Kilograms

Question 6

What is terminal velocity?

Answer 6

As an object falls through a fluid its acceleration decreases as it drag force increase the more the speed.Then the weight is balanced with the frictional forces and the resultant force is zero,then the velocity will be constant and it will fall at that speed.

Question 6

What’s newtons first law of motion?

Answer 6

According to Newton’s first law of motion, an object remains in the same state of motion unless a
resultant force
acts on it. If the resultant force on an object is zero also known inertia

Question 6

What is newton’s third law?

Answer 6

According to Newton’s third law of motion, whenever two objects interact, they exert equal and opposite forces on each other.

This is often worded as ‘every action has an equal and opposite reaction’.

Question 7

What direction does friction act on a moving object?

Answer 7

Opposite to the movement.

Question 7

What is the formula of stopping distance?

Answer 7

Stopping distance=thinking distance+braking distance

Question 8

What are factors affecting thinking distance?

Answer 8

Tiredness, drugs, alcohol, distractions and how fast the the car is going a the higher the velocity, the higher the thinking distance needed to stop the car.

Question 9

What are factors affecting breaking distance?

Answer 9

The road conditions, the car tyres and brakes as they might be worn out, the speed and mass of the car

Question 10

What is the formula for momentum

Answer 10

p=mv
momentum(kg/m/s)=mass(kg)*velocity(m/s)

Question 11

Momentum is a _____ quantity?

Answer 11

vector

Question 12

Momentum is also ________ what?

Answer 12

conserved as it is a closed system

Question 13

What happens in an elastic collision

Answer 13

the two objects bounce of each other

Question 14

What happens in a inelastic collision?

Answer 14

The objects stick to each other and move in the greater momentum direction.

Question 15

What happens in an explosion

Answer 15

The two objects move away from each other

Question 16

change in momentum formula?

Answer 16

Δp=mΔv

Question 17

What is the law of the conservation of momentum

Answer 17

total momentum before= total momentum after

Question 18

In an explosion what are the two objects momentum add up to

Answer 18

obj 1 momentum +obj 2 momentum =0
(The total momentum before is zero so by the law of conservation of momentum the momentum after is also zero.)

Question 19

What is the formula for impulse?

Answer 19

Impulse = forceTime
(newton seconds)

Question 20

What is impulse?

Answer 20

change in momentum

Question 21

In a collision, momentum is not always conserved WHy?

Answer 21

an external force acts (on the colliding objects)

Question 22

When a speed of a car is doubled why is the thinking distance doubled and why is the breaking distance more than doubled?

Answer 22

thinking distance proportional to speed
as reaction time is constant
when speed doubled and braking force constant, braking time greater
so braking distance more than doubles (think about area under
velocity–time graph)

Question 23

Example: Calculate the momentum of an 80kg rugby player running at 5m/s

Answer 23

80 kg × 5 m/s = 400 kg m/s

Question 24

A 60kg and an 80kg skater push away from each other.The 60kg skater moves away at 2.0m/s. a) Calculate her momentum and the other skater’s velocity

Answer 24

a)120 kg m/s
b)80v = 60 × 2.0 kg m/s
v = 60 × 2.0/80
= 1.5 m/s

Question 25

A 600kg cannon recoils at a speed of 0.5m/s when a 12 kg cannon balls leaves it.
Calculate the velocity of the cannon ball when it leaves the cannon.

Answer 25

12v = 600 × 0.5 kg m/s
∴ v = 600 × 0.5/12
= 25 m/s

Question 26

When a passenger wears a seat belt explain why it reduces the impact force?

Answer 26

seat belt increases time taken to stop person
so change of momentum per second less ∴ force on person less

Question 27

An 800kg car travelling at 30m/s breaks.Calculate the amount of breaking force required to stop the car in 6 seconds

Answer 27

Force = change of momentum/time taken =
800 kg × 30 m/s
6.0 s
= 4000 N

Question 28

What is meant by the limit of proportionality?

Answer 28

limit beyond which tension no longer proportional to extension

Question 29

What is the spring constant?

Answer 29

force per unit extension as long as limit of proportionality not reached

Question 30

What is hookes law?

Answer 30

extension of spring directly proportional to force applied as long as limit
of proportionality not exceeded

Question 31

What is the extension

Answer 31

increase in length from its original unstretched length