At MyTutor, we’ve got lots of dedicated Physics tutors across the UK who love helping teens achieve their best when exams come around. Since we started in 2013, we’ve given more than 250,000 one-to-one lessons, and over 1 million school pupils have used our online resource centre. Over time we’ve been able to get a strong understanding of exactly the topics in each subject that kids tend to need that extra help with.
Here are the top four Physics GCSE topics; where our students struggle most, and some example answers which can double as handy study notes for your child to get them revision-ready.
- What is the difference between Transverse and Longitudinal waves?
- What are the different ways that energy can be transferred?
- A bullet is fired horizontally from a rifle 1.5m from the ground at 430m/s. How far does it travel and for how long does it travel before it hits the ground? (Assuming that air resistance is negligible)
- How can an object accelerate without changing speed?
1. What is the difference between Transverse and Longitudinal waves?
Transverse Waves: Displacement of the medium is perpendicular to the direction of propagation of the wave.
To understand this it is good to think of a rope being held still by person B and being moved up and down by person A. The direction of propagation is from person A to B, so you will see the waves move along this way. But the displacement will be up and down.
Can travel in solids, but not in liquids and gas eg. Electromagnetic radiation
Longitudinal Waves: Displacement of the medium is parallel to the direction of propagation of the wave.
A good example for this is a slinky being pushed along the table, the propagation will be along the table and so will the displacement of all the ‘rings’. Can travel through all states of matter. eg. Sound waves.
2. What are the different ways that energy can be transferred?
There are three methods of energy transfer that we need to learn: conduction, convection, and radiation.
a) Conduction:
Heat is thermal energy, and in solids it can be transferred by conduction. Heat is passed along from the hotter end of an object to the cold end by the particles in the solid vibrating. The hotter particles vibrate a lot and cause the particles next to them to vibrate as they gain heat energy too. Solids are heat conductors due to how tightly packed their particles are.
For example: When a saucepan is put on a hob, overtime the handle will get hot too. Due to conduction -> the heat from the bottom of the pan will cause the particles to vibrate and then cause all the surrounding particles to vibrate until the handle is hot too.
b) Convection:
Fluids, that is both gases and liquids, can transfer heat energy by convection. It is easiest to explain this while thinking of an example:
Imagine a beaker of water being heated from the bottom. As the water particles at the bottom get hot, they expand and become less dense. This means they will rise to the top of the beaker, and other colder water particles will fall to replace them. After a while, the ‘new’ cold particles at the bottom will be heated and they will then rise to the top as they will be less dense. The water at the top which was first heated will have slightly cooled by then, so will sink down to the bottom, but then will be reheated and the same process will happen again.
This constant flow of the fluid due to the expansion / change in density of the particles is called a convection current. Over time all the fluid reaches a constant temperature.
c) Radiation:
Radiation is different to the other two processes as it doesn’t require particles in its transfer of energy. Instead, infra-red radiation is a type of electromagnetic radiation. This means that the energy is transferred by waves rather than particles.
Radiation is how we feel the heat from the sun on Earth, as waves can pass through the vacuum of space where there are no particles.
3. A bullet is fired horizontally from a rifle 1.5m from the ground at 430m/s. How far does it travel and for how long does it travel before it hits the ground? (Assuming that air resistance is negligible)
What’s important to realise about this question is that the horizontal velocity of the bullet makes no difference to how long it takes to fall to the the ground. Because the gun has not applied any vertical forces to the bullet, the only force affecting the bullet is gravity. This means the bullet takes just as long to fall to the ground as it would if it were dropped, despite it now travelling a large horizontal distance in the duration.
To find the travel time before hitting the ground we have 3 values:
- The displacement from the ground that the bullet must travel, s = 1.5m
- The acceleration the bullet experiences. As gravity is accelerating the bullet downwards, a = g = ~9.81m/s^2
- The initial velocity of the bullet vertically. As the bullet is stationary vertically (it is only travelling horizontally at the start), u = 0m
We examine our equations of motion, commonly known as SUVAT equations. You may need to learn these for your exam, but some examination boards provide them.
Because we have s, u and a, and we are looking for the time t, the relevant equation is
s = ut + 0.5(at^2)
Filling in our values we have:
1.5 = 0t + 0.5(9.81 x t^2)
1.5 = 4.905 x t^2
Divide 1.5 by 4.905 to find t^2
t^2 = 0.3058…
We simply find the square root of t^2 to find t, the time taken for the bullet to reach the ground:
t = 0.553s (3 significant figures)
To find the horizontal distance, d, that the bullet has travelled before it has hit the ground we can use the equation linking displacement s with some velocity v over some time duration t:
s = vt
The horizontal velocity of the bullet, v = 430
The time before the bullet hits the ground, t = 0.553
So d = vt = 430 * 0.553 = 238m (3 significant figures)
4. How can an object accelerate without changing speed?
Acceleration is defined as the rate of change of velocity.
Since velocity is a vector quantity (it has both magnitude and direction) defined as speed in a particular direction, any change in either speed or direction of travel is a change in velocity.
Acceleration therefore occurs whenever an object changes direction. For example, a car driving around a roundabout is constantly accelerating even if its speed does not change.
Good luck! You can find your own Physics tutor to get personalised one-to-one help today.