Physics Questions & Answers - Physics Doubts, Problems, Homework Solutions

Define Newton's three laws

1st Law - a body will move with constant velocity or remain at rest unless acted on by a resultant force
2nd Law - F = ma. The rate of …

Which is heavier, a ton of feathers or a ton of lead?

They're both the same. The feathers would take up a lot more space though! Feathers have a lower density than lead (i.e. for the same volume, feathers are less heavy). …

If a box full of feathers and a box full of bricks were to be dropped at the same time and from the same height, which one would hit the ground first?

They would hit to ground at the same time. This is because they would both accelerate to the ground at 10m/s^2 due to gravity regardless of what their mass is. …

A car of mass 1000 kg is travelling at 15 m/s. The driver applies the brakes for 4 seconds, slowing the car to 5 m/s. What is the average power output of the brakes over the 4 seconds? Assume there are no other forces acting on the car.

Kinetic Energy, EK=(1/2)mv2. Energy is conserved, so the work done by the brakes, W, must be equal to the change in kinetic energy of the car, ∆EK. Therefore: …

What are the 3 main types of radiation?

The three main types of radiation are alpha, beta and gamma radiation. Alpha particles are the largest, two protons and two neutrons bound together (so they have a +2 positive …

An electric whisk in a bakery has two motors, each with an average power of 1500W. The whisk is used for 4 hours each day, 7 days a week. Electricity costs 18p per kilowatt-hour. Calculate the cost of the electricity used by the whisk in one week.

First, we must calculate the amount of time spent using the whisk in one week:4 x 7 = 28 hours a weekNext we calculate the power used; as the whisk …

Explain what terminal velocity means.

Consider an object in free fall through the atmosphere. Firstly, we need to consider the forces acting on the object. A force diagram will help here. Weight acts from the …

An apple is suspended a string and a spring in parallel. When the string is cut, the apple falls, and the spring stretches and contracts repeatedly as the apple bounces. Describe the energy conversions that occur during this process.

When the string is cut:Gravitational potential energy is converted to kinetic energy.Kinetic energy is converted to elastic potential energy.Elastic potential energy is converted to kinetic energy (and heat energy)Kinetic energy …

Describe how you could find the density of a cube of metal? (4 marks) (Example from GCSE bitesize)

  1. Think of key words in the questions to help solve it. For example in this question we need to consider density and the fact that the object is a cube. …

What is the difference between velocity and speed?

Both the speed and the velocity show us how fast something is moving (the rate at which it changes its position). However, velocity is a vector quantity, which means it …

calaculate the resistance if two 3 ohm resitsors are placed in series and another 3 ohm was attached in parallel

total resistance for resistors in series is the addition of the resistances therefore the two 3 ohm resisters in series totals 6 ohms resistors in parallel follow the equation : …

What is cosmic microwave background, and where does it come from?

Cosmic microwave background is a very faint level of microwave radiation filling all of space, and coming from all directions. The cosmic microwave background is useful to physicists as it …

A boy with a mass of 50kg is sitting on a seesaw. He is sitting 2m from the pivot. He has a friend who weighs 40kg, how far away from the pivot must she sit to balance the seesaw? (gravitational accelleration (g) = 10m/s2)

This is a question relating to turning forces, known as moments. For the seesaw to be balanced the moment caused by the 50kg boy must be equal and opposite …

Explain Ohms Law

Ohms law establishes a relationship between resistance, voltage and current, saying that V/I = R. The traditional graph given for ohmic resistors is:An increasing line with gradient x starting at …

A block of mass 5kg is placed on the end of a meter rule on the end of a table. Calculate the moment that is produced by the block.

1.Moment=Force x Distance2.Convert mass into weight (x9.81)3.Times the weight by the distance from the pivot point.4.If done correctly the answer should be 49.06NKg …

what is ohm's law?

Ohms law establishes a relationship between resistance, voltage and current, saying that V/I = R.

What is the difference between displacement and distance?

Let's suppose tomorrow we want to go to the Moon. There's many different paths that we can choose from to get there: we can depart from Earth, go around the …

A force of 13.8 N was used to lift a mass 30 cm vertically through a liquid. Calculate the work done in lifting the mass, stating the correct units.

Either from memory or using the formula booklet provided we know Work Done = Force x Distance Moved (in the direction of the force). Therefore we can use the values …

What is refraction?

Refraction is what occurs when light passes from one medium to another (for example, air to water) and because of the difference in the medium, the speed changes. This change …

Explain why evaporation cools a liquid.

Evaporation occurs when the most energetic particles in a liquid have enough energy to overcome the attractive intermolecular bonds and leave the liquid. Because only the hughest energy particles evaporate …