mechanics

• Velocity of an object at maximum height

  0
• If the angle of a force vector is 45


  the vertical and horizontal components are equal
• 2 bullets are fired simultaneously. The second bullet has a lower initial velocity than the first bullet. Explain why the horizontal displacement of the first bullet will be greater than the second bullet


  vertical acceleration for both bullets is the same, both bullets will be in the air for the same time, horizontal acceleration is zero and thus, s = u t where u is the horizontal velocity
• Calculate the acceleration from a distance time graph of uniform acceleration

  suat equation
• State and explain what happens to the gravitational potential energy lost when going down a slope at constant velocity

  all the energy is transferred into the thermal store of surroundings due to air resistance
• How to calculate the component of the weight on a slope?

  wsinθ
• Why does no device ever have an efficiency of 100%?


  some energy is always dissipated
• Define efficiency

  measure of how much energy is transferred usefully
• Define high power

  lots of energy transferred in a short time
• What is power measured in?


  watts (W)
• Define power


  the rate of work done
• What is work done measured in?

  joules (J)
• Define work done


  the energy transferred when a force moves an object through a distance
• Adapt the equation of P = Fv for when force and motion are in different directions

  P =Fvcosθ where, θ = angle at which the force acts from the direction of motion
• Explain how air bags in cars are designed to help protect passengers in a crash

  slow down passengers more gradually and prevent them from hitting hard surfaces inside the car
• Explain how seat belts in cars are designed to help protect passengers in a crash

  stretch slightly, increasing the time taken for the wearer to stop. This reduces the force acting on the chest
• Explain how crumple zones in cars are designed to help protect passengers in a crash

  at the front and back of cars, crumple up and deform plastically on impact. This causes the car to take longer to stop increasing the impact time and decreasing the force on the passengers
• What is Newton's second law in terms of momentum?

  F = Δ(mv) / Δt
• Define Δ(mv) as an equation


  mv - mu
• Formula for momentum


  p=mv
• Define impulse


  change in momentum Δ(mv), FΔt
• How does a skydiver reduce their terminal velocity?

  using a parachute to increase the drag they experience
• If the weight on a scale is less than the person's weight when standing in a lift is the lift accelerating or decelerating?

  decelerating
• In what direction does a lift force act, relative to a flowing fluid?

  perpendicular to the direction the fluid is flowing
• Define drag

  name given to friction caused by a fluid
• Define friction

  force that opposes motion, acts in the opposite direction to the motion
• Other than by increasing the power of the engine, how could the maximum speed of the car be increased?

  changing the shape of the car to be more streamlined, this lowers the air resistance on the car
• Describe the graph for acceleration vs time for the terminal velocity situation

  negative gradient outward curve flattens into a horizontal line
• Describe the graph for velocity vs time for the terminal velocity situation

  positive gradient outward curve flattens into a horizontal line
• What is the effect of air resistance on the trajectory of a projectile?

  reduces horizontal speed, horizontal distance, maximum height and steepens the angle of descent
• For projectile motion at an angle which component do you use to find time?

  vertical, height x 2 as reaches 0ms⁻¹ at maximum height
• Define projectile motion

  freefall motion where the object is given an initial velocity
• Explain how you can plot data obtained from an experiment to determine the value of g on a graph

  plot a graph of height vs the time it takes the ball to fall, squared. Draw a line of best fit and multiply the gradient by 2 to get a value for g
• Describe an experiment you could do to obtain data that you could use to determine the value of g

  Measure the height from the bottom of the ball bearing to the trapdoor. Flick the switch to simultaneously start the timer and disconnect the electromagnet, releasing the ball bearing. The ball bearing will fall , knocking the trapdoor down and breaking the circuit which stops the timer. Record the time shown on the timer. Repeat this experiment 3 times and average the time taken to fall from this height. Repeat this experiment but drop the ball from several different heights
• Give 2 ways systematic errors can be reduced when carrying out an experiment to determine the value of g that measures the length of time an object takes to fall a set distance

  use a small, heavy ball to negate the effect of air resistance and have a computer automatically release and time the ball-bearing's fall
• Why does a bird lift into the air when it flaps its wings?

  when a bird flaps its wings it pushes down on the air. The air then pushes back up on the bird's wings with the same force, which causes it to lift
• What must you draw when asked to draw a diagram showing what forces are acting on a book when its sitting still on the floor?

  an upwards arrow on the book labelled 'floor pushes upwards on book' and a downwards arrow on the book labelled 'gravity pulls down on the book
• Describe the motion of an object when there is a straight line with a positive gradient beneath the x axis on an acceleration-time graph?

  the object is slowing down
• What value can be calculated using a tangent on a displacement-time graph?

  instantaneous velocity
• How would you describe what's happening in a displacement time graph?

  The (object) (is/isn't) moving (forwards/back towards the starting point) (at a constant velocity/but (ac/de)celerating)