Booklet 1A - Dynamics (Factual)

Question 1

What is the difference between a vector and a scalar?

Answer 1

Scalar requires size (magnitude) only

Vector requires size (magnitude) and direction

Question 2

Which of the following are scalars? Time, Momentum, Acceleration, Energy, Speed, Velocity, Displacement, Distance, Force

Answer 2

Scalars: Time, Energy, Speed, Distance

Question 3

Which of the following are vectors? Mass, Weight, Momentum, Impulse, Work, Temperature, Acceleration, Velocity, Speed

Answer 3

Vectors: Weight, Momentum, Impulse, Acceleration, Velocity

Question 4

What is the difference between distance and displacement?

Answer 4

Distance is the length of the actual path travelled, Displacement is the straight line distance between where you started and where you finished, with a direction.

Question 5

What is the difference between speed and velocity?

Answer 5

Speed is distance divided by time (OR rate of chage of distance) and is a scalar.

Velocity is the displacement divided by time (OR rate of change of displacement) and is a vector, i.e. has a direction.

Question 6

What is speed?

Answer 6

Change in distance per second (OR rate of change of distance).

Question 7

What is velocity?

Answer 7

Change in displacement per second (OR rate of change of displacement).

Question 8

What is acceleration?

Answer 8

Change in velocity per second (OR rate of change of velocity).

Question 9

Describe an experiment to measure the acceleration of a trolley in a lab.

Answer 9

Ensure that the mask cuts the light gates. Measure the length of the mask (d) using a ruler. Using the timer measure the times for the mask to cut the first light gate (t1), the second light gate (t2) and the time for the mask to travel between light gates (t). Calculate the initial velocity (u) using u=d/t1 and the final velocity (v) using v=d/t2. Calculate the acceleration (a) using a = (v-u)/t.

Question 10

What is calculated from the area under a speed-time graph?

Answer 10

Distance travelled

Question 11

What is calculated from the area under a velocity - time graph?

Answer 11

Displacement

Question 12

What is calculated from the gradient of a displacement-time graph?

Answer 12

Velocity

Question 13

What is calculated from the gradient of a velocity-time graph?

Answer 13

Acceleration

Question 14

A ball is thrown upwards into the air and is allowed to fall and bounce. See graph.

Between which points on the graph is the ball travelling upwards?

Answer 14

A-B, D-F,

Question 15

A ball is thrown upwards into the air and is allowed to fall and bounce. See graph.

Between which points on the graph is the ball hitting the ground?

Answer 15

C-E, G-I

Question 16

A ball is thrown upwards into the air and is allowed to fall and bounce. See graph.

At which points is the ball at the top of it’s flight?

Answer 16

B, F

Question 17

What is Newtons First Law?

Answer 17

An object will remain at rest or continue to travel at a constant velocity (i.e. in a straight line) unless an unbalanced forces acts on it.

Question 18

What is Newtons Second Law?

Answer 18

F_un = ma

i.e. when an unbalanced force acts on an object it will accelerate.

Question 19

What is the definition for 1 Newton?

Answer 19

One newton is defined as the force required to make a 1kg object accelerate at 1ms^-2.

Question 20

Explain what would happen to your apparent weight (the reading on a set of Newton scales) if you were standing on them in a lift that was accelerating upwards?

Answer 20

Your apparent weight would increase, It would be equal to your weight plus the force to cause the acceleration upwards.

Question 21

Explain what would happen to your apparent weight (the reading on a set of Newton scales) if you were standing on them in a lift that was travelling at a constant speed.

Answer 21

Your apparent weight would = real weight as the forces are balanced.

Question 22

Explain what would happen to your apparent weight (the reading on a set of Newton scales) if you were standing on them in a lift that was deccelerating upwards?

Answer 22

Your apparent weight would decrease, It would be equal to your weight minus the force to cause the de-acceleration upwards.

Question 23

Explain what would happen to your apparent weight (the reading on a set of Newton scales) if you were standing on them in a lift that was deccelerating downwards?

Answer 23

Your apparent weight would increase, It would be equal to your weight plus the force to cause the de-acceleration downwards.

Question 24

Explain what would happen to your apparent weight (the reading on a set of Newton scales) if you were standing on them in a lift that was accelerating downwards?

Answer 24

Your apparent weight would decrease, It would be equal to your weight minus the force to cause the acceleration downwards.

Question 25

Explain the increase in acceleration when a rocket is taking off.

Answer 25

As the rocket burns fuel, its mass (m) decreases. This causes the weight (W = mg) to decrease and so the unbalanced force to increase (F_un = Thrust - W). The increase in F_un and decrease in m both cause the acceleration to increase since a = F_un/m. If the rocket is moving away from a planet there will also be a decrease in the gravitational field strength (g) causing a further decrease in weight.

Question 26

Explain how an object reaches it's terminal velocity.

Answer 26

The weight of the object acts as a downwards unbalanced force which by Newton's 2nd law results in downwards acceleration. As the object speeds up, the opposing air resistance will increase. Eventually the air resistance balances the weight. By Newton's First Law balanced forces result in a constant velocity, known as the terminal velocity. An increase in surface area (e.g. opening a parachute) will cause an increase in air resistance, meaning there is now an upwards unbalanced force and the object will deccelerate by Newton's 2nd law. This slowing down decreases the air resistance until it once again balances the weight and a new slower terminal velocity is reached.

Question 27

A velocity-time graph for a parachutist is shown below. Identify when the parachute open.

Answer 27

B

Question 28

A velocity-time graph for a parachutist is shown below. Between what points is terminal velocity without the parachute open reached?

Answer 28

Between A' and B

Question 29

A velocity-time graph for a parachutist is shown below. Between what points is terminal velocity with the parachute open reached?

Answer 29

Between C' and D

Question 30

What is the resultant of a number of forces?

Answer 30

the single force that would have the same effect as all the other forces (OR the vector sum of all the forces)

Question 31

What formula is used to work out the component of weight parallel to the slope?

Answer 31

F = mgsinθ

Question 32

State what is meant by the Principle of Conservation of Energy?

Answer 32

Energy cannot be created or destroyed, only converted from one form to another.

Question 33

What is the Law of Conservation of Linear Momentum?

Answer 33

The total momentum before a collision is equal to the total momentum after a collision in the absence of net external forces

Question 34

What quantity is always conserved in a collision?

Answer 34

Momentum

Question 35

How can an inelastic collision be identified?

Answer 35

**_Kinetic energy is lost_** - the total kinetic energy before the collision is greater than the total kinetic energy after the collision.

Question 36

How can an elastic collision be identified?

Answer 36

The total kinetic energy before the collision IS equal to the total kinetic energy after the collision.

Question 37

What is the definition of Impulse

Answer 37

Force on an object multiplied by the time the force acts for OR the change in momentum of an object.

Question 38

Which two units can be used for momentum?

Answer 38

Ns OR kgms^-1

Question 39

What can be calculated from the area under a Force - time graph?

Answer 39

Impulse (OR Change in momentum)

Question 40

A brick is dropped first onto concrete then onto a sponge surface. The same brick is dropped and it is dropped from the same height. On which surface does the brick exert the smallest force? Explain your answer.

Answer 40

As the brick is dropped from the same height, it will start from rest in both cases and reach the same speed before it hits the surface. The change in momentum remains the same, mv-mu. The time of contact will increase on the spongy surface. Ft = mv-mu So the **average force** will decrease.

Question 41

Two identical balls (1 and 2) are dropped from the same height and come to a halt without bouncing. By comparing the force-time graphs below explain which ball landed on water and which in concrete. Explain the graphs for ball 1 and 2 have in common?

Answer 41

Ball 1 lands on concrete (a hard surface) and ball 2 on water (a soft surface). We know this because ball 1 takes less time to come to a stop than ball 2, meaning the peak force is larger. Both graphs would have the same area-under-graph because they have the same change in momentum (Δp) when stopping since they have identical values of mass (m), final velocity (v) and initial velocity (u) and Δp = mv - mu