Motion Basics
What unit is most commonly used to measure speed and acceleration
Speed - m/s
Acceleration - m/s2
A student walks 100 m in 20 s. Calculate their speed.
100/20 = 5 m/s
A box has a 50 N force pushing right and a 30 N force pushing left. What is the net force and direction of the that the box moves?
20 N right
Identify the energy transformation that occurs when a hand-held torch is switched on.
Chemical (battery) --> electrical --> light & heat
What is the difference between distance and displacement?
Distance is the total length of the journey travelled
Displacement is the change in position from the starting point (includes direction)
A car changes velocity from 5 m/s to 15 m/s in 5 s. Calculate the acceleration.
15-5 = 10 m/s
10/5 = 2 m/s2
What happens to the movement of an object when forces are...
Balanced
Unbalanced
Balanced - motion does not change (remains stationary or continues at constant velocity)
Unbalanced - motion will change based on the stronger force
Calculate...
1) Calculate the kinetic energy of a 2 kg object travelling at 4 m/s
2) Calculate the gravitational potential energy of a 5 kg object raised 10 m above the ground
1) 0.5 x 2 x 4 = 4 J
2) 5 x 9.8 x 10 = 490 J
A runner leaves home and travels in a 6 km north before turning around and running 4 km south to meet a friend.
What is their distance and displacement?
Distance - 10 km
Displacement - 2 km north
A car travels 150 km at an average speed of 20.8 m/s. Calculate the time taken for this journey in hours.
20.8 x 3.6 = 74.88 km/h
150/74.88 = 2 hours
State Newton's 3 laws
First - object will remain at rest or travel at constant speed unless acted upon by external force
Second - object will accelerate in the direction of an unbalanced force (F = m x a)
Third - every action has an equal and opposite reaction
Which of the options below has more kinetic energy? Give evidence to support your answer
1 kg at 20 m/s
1 kg at 20 km/h
1 kg at 20m/s has more kinetic energy
0.5 x 1 x 20 = 10 J
20/3.6 = 5.56 m/s --> 0.5 x 1 x 5.56 = 2.78 J
What is the differenc between average speed and instantaneous speed?
Average speed is the total distance travelled divided by the total time
Instantaneous speed is the speed at one particular moment
Draw a ticker tape to show the following scenarios...
object accelerating
object decelerating
stationary object
object accelerating - dots progessively further apart
object decelerating - dots progressively closer
stationary object - dots in one place
Complete these calculations...
1) A 5000 g object accelerates at 4 m/s2. What is the force?
2) A force of 200 N accelerates an object at 5 m/s2. What is its mass?
1) 5000 g = 5 kg
5 x 4 = 20 N
2) 200/5 = 40 kg
A rollercoaster car and passengers has a combined mass of 750 kg. At the top of the first hill, it is approximately 32 m above the ground. Determine the gravitational potential energy at the top of the hill, and estimate the kinetic energy as it falls to the bottom of the hill.
Draw a freebody diagram as it moves down the hill
GPE = 750 x 9.8 x 32 = 235 200 J (100 points)
KE = approximately 235 200 J (100 points)
Freebody diagram to include gravity, friction, air resistance (200 points)
A cyclist rides 6 km in 15 minutes.
Calculate their speed in km/h and in m/s
15/60 = 0.25 hours
6/0.25 = 24 km/h
24/3.6 = 6.67 m/s
A cyclist starts from rest and accelerates uniformly to 12m/s over 6 seconds. The cyclist then continues at 12 m/s for 2 seconds and then slows down uniformly to rest over 4 seconds.
Draw a velocity time graph and calculate the total distance travelled
100 - axis labels correct
100 - axis scalled correctly
100 - data plotted correctly
200 - total distance calculated correctly
A swimmer pushes water backwards to move forwards. Identify and explain which on of Newton's Laws is being described here.
Newton's third law
As the swimmer pushes water backwards, the water pushes against the swimmer with equal fore causing them to move forwards
A lightbulb is 70% efficient with some energy being wasted as heat. It recieves 800 J of energy. Calculate the useful energy output and draw a Sankey diagram for this.
800 x 70% = 560 J
Sankey --> 800 J going in, 560 J straight out as useful light energy. Slightly smaller arrow 240 J being lost as wasted heat energy below