Topic 5 : Forces

Question 1

True or false? Scalar quantities only have a magnitude

Answer 1

True

Question 2

Name two vector quantities

Answer 2

Any of : force, velocity, displacement, acceleration, momentum, weight, drag

Question 3

When contact forces act between a pair of interacting objects, what must be true about the two objects?

Answer 3

They must be physically touching for contact forces to act

Question 4

Describe the pair of forces that act in the interaction between the earth and the moon

Answer 4

The gravitational force of the earth is felt by the moon and the gravitational force of the moon is felt by the earth. The forces of attraction are equal and opposite.

Question 5

What is meant by the weight of an object?

Answer 5

The force acting on an object due to gravity

Question 6

What’s the formula for calculating the weight of an object?

Answer 6

Weight = mass * gravitational field strength or W = mg

Question 7

The weight of a uniform object can be assumed to act at a single point. What is this single point called?

Answer 7

The object’s centre of mass

Question 8

What is a newtonmeter used to measure?

Answer 8

Weight or force

Question 9

True or false? The forces that act on an object can be replaced with a single resultant force that has the same effect

Answer 9

True a resultant force can replace forces that are acting on a single object/point

Question 10

How do you calculate the magnitude of the resultant force of two forces acting on an object in the same direction?

Answer 10

Add the magnitudes of the two forces together

Question 11

All the forces acting on an object are balanced. What is the resultant force?

Answer 11

Zero

Question 12

What does it mean to ‘resolve’ a single force?

Answer 12

Split the force into its components.

Question 13

If an object is in equilibrium, what must be true about all the forces acting on the object?

Answer 13

They must be balanced. You could also say that they must combine to give a resultant force of zero

Question 14

What is the word equation used to calculate work done on an object moved by a force?

Answer 14

Work done = force * distance

Question 15

One newton metre is equal to how many joules?

Answer 15

1 newton metre = 1 joule

Question 16

What’s the equation that links extension, force and spring constant?

Answer 16

Force = spring constant * extension or F = Ke

Question 17

If an object is balanced ,what must be true about the total clockwise and total anti clockwise moments?

Answer 17

They must be equal

Question 18

True or false? The moment of force will increase when transferred from a larger gear to a smaller one

Answer 18

False. (The moment will decrease because on the smaller gear, the distance from the pivot to the line of action of the force is smaller)

Question 19

True or false? A gas is a type of fluid

Answer 19

True. A fluid that is exerted at the right angles to a surface

Question 20

Explain why the pressure of water increases with depth

Answer 20

The greater the depth, the more water particles there are there above that point. This means the total weight of particles above that point is greater, so the pressure is greater

Question 21

What is the earths atmosphere?

Answer 21

A thin layer of air that surrounds the earth

Question 22

Explain why a submerged object experiences upthrust in terms of fluid pressure

Answer 22

A submerged object experiences a force on all surfaces as a result of the pressure of the fluid. Because pressure is greater with depth, the force experienced at the bottom of the object is greater than at the top. This means the resultant force is upwards

Question 23

True or false? Moving objects usually travel at a constant speed

Answer 23

False. In the real world the speed of a moving object is rarely constant

Question 24

True or false? A negative change in speed shows the object has decelerated

Answer 24

True. A negative change in speed gives a negative acceleration, which is deceleration

Question 25

What are Newton’s 1st, 2nd and 3rd Laws of Motion?

Answer 25

1) a resultant force is needed to make something start moving, speed up, or slow down (stationary object remains stationary if the resultant force on it is zero. Moving object carries on moving at same velocity - speed and direction - if resultant force on it is zero)
2) acceleration is proportional to the resultant force Resultant force F (N) = Mass M(kg) * Acceleration (m/s2)
3) when two objects interact, the forces they exert on each other are equal and opposite

Question 26

What is inertia?

Answer 26

Inertia is the tendency for motion to remain unchanged. / the tendency of objects to continue in their state of rest or of uniform motion

Question 27

What is meant by the ‘braking distance’ of a car?

Answer 27

The distance the car travels under the braking force once the brakes are applied

Question 28

What is the difference between scalar quantities and vector quantities?
Give two examples of each

Answer 28

‘Vector quantities have a magnitude (size) and a direction - force, velocity, displacement, weight, acceleration, momentum
Scalar quantities only have magnitude, not direction - mass, speed, distance, energy, temperature, time

Question 29

A) Give a word equation for distance, speed and time
B) If a sprinter runs 200m in 25s what is his average speed?

Answer 29

Distance travelled (m) = average speed (m/s) * time (s)

200=average speed * 25, so average speed = 200/25 = 8m/s

Question 30

Define acceleration in terms of velocity and time

Answer 30

Acceleration (m/s2) = (initial velocity m/s - final velocity m/s)
______________________________
Time (s)

Question 31

What does the gradient represent for
A) a distance/ time graph
B) a velocity/ time graph

Answer 31

A) in a distance m/ time s graph gradient = slope and gives speed - steeper the slope is more distance in smaller time = faster
B) in a velocity m/s/ time s graph gradient = acceleration - steeper the slope is more acceleration or deceleration

Question 32

How do you find the distance travelled by an object from a velocity/ time graph?

Answer 32

The area under any section of the graph (or all of it) - where the gradient line is constant split into rectangles and triangles

Question 33

What is stopping distance made up of?
Why should drivers on long distances take regular breaks

Answer 33

Stopping distance = thinking distance + braking distance

The longer it takes a car to stop after seeing a hazard, the higher the risk of crashing/ injuries.
Thinking distance is distance travelled in driver’s reaction time (ie between noticing a hazard and applying breaks) Reaction time increased by tiredness and distractions (caused by boredom or other influences).
The faster you are travelling, the further you travel during reaction time. Regular breaks improves alertness and concentration on appropriate speed for road conditions, weight of vehicle’s load and condition of tyres and brakes.