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Physics module 4…read more

Slide 2

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Equations to remember
Distance = speed x time
E.g. A car travels at a distance of 100 metres in 20 seconds. What is the speed of the car?
Distance ÷ time = speed
100 ÷ 20 = 5
Answer = 5m/s
Mass x Velocity = momentum
E.g. A 65kg man is running at 10m/s in a straight line. Calculate its momentum
Momentum = mass x velocity
65 x 10
answer = 650 kg m/s
Change of momentum = resultant force x time (for which the force acts)
E.g. A rock with a mass of 1kg is travelling through space at 15 m/s. A comet hits the rock, giving
it a resultant force of 2500 N for 0.7 seconds. Calculate the rock's initial momentum, then its
change in momentum after the impact.
Momentum = mass x velocity
1 x 15 = 15 kg m/s
Change of momentum = resultant force x time
2500 x 0.7 = 1750 kg m/s…read more

Slide 3

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More equations
Change in energy = Work done
Work done (J) = Force (N) x Distance (m)
E.g. Someone drags a tyre 5 m over flat ground. They pull with a total force of 340 N.
Find the work done.
Work done = force x distance
340 x 5 = 1500 J
Kinetic Energy = ½ x mass x velocity²
E.g. A car with a mass of 2450 kg is travelling at 38 m/s.
Calculate its kinetic energy.
Kinetic Energy = ½ x mass x velocity²
½ x 2450 x 38² = 1,768, 900 J
Gravitational potential energy = weight x change in height
E.g. A 4000 N car is thrown into the air 10m. Calculate its change in G.P.E.
Gravitational potential energy = weight x change in height
4000 x 10 = 40,000 J (40 KJ)…read more

Slide 4

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Distance-Time Graphs
· Gradient = Speed
· The flat sections indicate where the object has stopped
· If the graph is steeper, the object is travelling faster
· When the line is descending, the object is going towards the
starting point
· Curves represent acceleration or deceleration
Gradient = vertical ÷ horizontal
· Distance time graphs can be positive and negative
· The object is going in a different direction past the
starting point if the graph goes to negative numbers…read more

Slide 5

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Velocity-Time Graphs
· Gradient = acceleration
· Flat sections represent steady speed
· The steeper the graph, the faster the acceleration or deceleration
· The area under the graph = distance travelled in that time
· Curves mean changing acceleration…read more

Slide 6

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Forces & Friction
· Interaction pairs ­ If an object exerts a force on another object, the 1st object will
experience an opposing force.
· For example, if you lean on a wall, the wall will push back against you. As soon as
you stop pushing against it, the wall stops pushing against you. The force the wall
exerts on you is called a reaction force.
· The same happens if you pull an object ­ the object will exert the exact opposite
force on you.
· Friction ­ If an object is sliding over another object, both objects will experience a
force in the direction that opposes the movement.
· The green and blue arrows show an
interactive pair.…read more

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