Booklet 1A - Dynamics (Factual) Flashcards
What is the difference between a vector and a scalar?
Scalar requires size (magnitude) only
Vector requires size (magnitude) and direction
Which of the following are scalars? Time, Momentum, Acceleration, Energy, Speed, Velocity, Displacement, Distance, Force
Scalars: Time, Energy, Speed, Distance
Which of the following are vectors? Mass, Weight, Momentum, Impulse, Work, Temperature, Acceleration, Velocity, Speed
Vectors: Weight, Momentum, Impulse, Acceleration, Velocity
What is the difference between distance and displacement?
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.
What is the difference between speed and velocity?
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.
What is speed?
Change in distance per second (OR rate of change of distance).
What is velocity?
Change in displacement per second (OR rate of change of displacement).
What is acceleration?
Change in velocity per second (OR rate of change of velocity).
Describe an experiment to measure the acceleration of a trolley in a lab.
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.
What is calculated from the area under a speed-time graph?
Distance travelled
What is calculated from the area under a velocity - time graph?
Displacement
What is calculated from the gradient of a displacement-time graph?
Velocity
What is calculated from the gradient of a velocity-time graph?
Acceleration
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?
A-B, D-F,
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?
C-E, G-I
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?
B, F
What is Newtons First Law?
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.
What is Newtons Second Law?
Fun = ma
i.e. when an unbalanced force acts on an object it will accelerate.
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?
Your apparent weight would increase, It would be equal to your weight plus the force to cause the acceleration upwards.
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.
Your apparent weight would = real weight as the forces are balanced.
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?
Your apparent weight would decrease, It would be equal to your weight minus the force to cause the de-acceleration upwards.
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?
Your apparent weight would increase, It would be equal to your weight plus the force to cause the de-acceleration downwards.
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?
Your apparent weight would decrease, It would be equal to your weight minus the force to cause the acceleration downwards.
Explain the increase in acceleration when a rocket is taking off.
As the rocket burns fuel, its mass (m) decreases. This causes the weight (W = mg) to decrease and so the unbalanced force to increase (Fun = Thrust - W). The increase in Fun and decrease in m both cause the acceleration to increase since a = Fun/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.
Describe Tension
Tension is a pulling force exerted by a string or cable on another object
Explain how an object reaches it’s terminal velocity.
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.
A velocity-time graph for a parachutist is shown below. Identify when the parachute open.
B
A velocity-time graph for a parachutist is shown below. Between what points is terminal velocity without the parachute open reached?
Between A’ and B
A velocity-time graph for a parachutist is shown below. Between what points is terminal velocity with the parachute open reached?
Between C’ and D
What is the resultant of a number of forces?
the single force that would have the same effect as all the other forces (OR the vector sum of all the forces)
What formula is used to work out the component of weight parallel to the slope?
F = mgsinθ
State what is meant by the Principle of Conservation of Energy?
Energy cannot be created or destroyed, only converted from one form to another.
What is the Principle of Conservation of Linear Momentum?
The total momentum before a collision is equal to the total momentum after a collision in the absence of net external forces
What quantity is always conserved in a collision with no net external forces?
Momentum
How can an inelastic collision be identified?
Kinetic energy is lost - the total kinetic energy before the collision is greater than the total kinetic energy after the collision.
How can an elastic collision be identified?
The total kinetic energy before the collision IS equal to the total kinetic energy after the collision.
What is the definition of Impulse
Force on an object multiplied by the time the force acts for OR the change in momentum of an object.
Which two units can be used for momentum?
Ns OR kgms-1
What can be calculated from the area under a Force - time graph?
Impulse (OR Change in momentum)
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.
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.
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?
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
