Q&A for How to Calculate Kinetic Energy

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What is the kinetic energy possessed by a car having a mass of 1500 kg and travelling at a velocity of 50 km/h?

Community Answer

Recalulate 50 km/h into m/s which is 13.889 m/s; then apply the formula: KE = 0.5 * 1500kg * (13.889 m/s)^2 = 144678 J => appr. 145 kJ

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If mass and velocity of body is doubled how can I figure out the change in kinetic energy?

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The formula given for K.E. is K.E. = 0.5m(v^2). Doubling mass gives m = 2m. Doubling velocity gives v^2 = (2v)^2 =4v^2. Which makes K.E. 4 x 2 = 8 times bigger in total.

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What if the amount is in grams?

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If it's in grams, you'll have to convert it to kilograms by dividing it by 1000. For example, 100g becomes 0.1kg, and 3g becomes 0.003kg.

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What is the force of a mass dropped from a height?

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A mass dropped from a height will be in freefall. The force will be its weight, mg, where g = 9.81 m/s^2.

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Question

Why is it that the example in our textbook is ke=1/2 mv^2?

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Community Answer

Because 0.5 and 1/2 are equal. (mv^2)/2 would also be the same equation.

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When do I use KJ in K.E?

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You use KJ in K.E. when the answer is bigger than 1000 J. 1000 J is the same as 1 KJ. So, for example, when the answer is 2635 J, you could write this down as K.E. = 2.635 KJ, or approximately 2.6 KJ.

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If a 100-kilogram crate is dropped into the sea from a height of 2 meters, what is the kinetic energy?

Community Answer

The law of conservation of energy shows us that the maximum amount of energy at any point will not change regardless of how much of each type of energy is present, so if at maximum height, where only potential energy is present we calculate the energy as (100)(2)(-10)= 2000J, then the kinetic energy at max or right before the crate hits the water will also be 2000J.

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Question

How do I calculate the potential energy of a falling mass?

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Falling mass is purely kinetic. The potential energy is 0. Since potential and kinetic are opposites, when one is maxed, the other is 0. So, when the object is at its fastest speed, there is no potential energy.

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How do I calculate momentum?

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Community Answer

Momentum of any body can be defined as the product of Mass of that body to the its velocity. Momentum is identified by symbol P so P=m*v.

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How do I convert km/h into m/s?

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1 km/h is equal to 0.277778 m/s. So you should be able to just multiply your km/h by 0.277778.

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What is the kinetic energy if the mass is 5kg and 10 meters from the ground?

Community Answer

E = m*g*h = 5*9.81*10 where g is the gravitational acceleration on earth in m/s^2, m is mass in kg and h is height in meters.

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Question

How do I find KE without knowing KE or velocity and only knowing the mass?

Community Answer

You cannot. You have 2 unknowns, so without more information you cannot determine KE.

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Question

What is the kinetic energy available in a channel 1.85m wide x 0.8m deep flowing at 0.4m/s?

Cabbache

Community Answer

Imagine the fluid as segments of blocks, each with a volume of 1.85mx0.8mx0.4m. Each of these blocks move 0.4m every second. Assuming the fluid is water of density 1000Kg/m^3, then the mass of the block is 592Kg. now you can use K.E = mv^2 / 2. 592 x 0.4 x 0.4 / 2 = 47.36 Joules.

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How do I determine how far something will travel if I know the kinetic energy and force?

Cabbache

Community Answer

The question is not clear, but I would say work done = force x distance, so divide the kinetic energy by the force.

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Why is it important to calculate kinetic energy?

Community Answer

Kinetic energy is important as a tool in the macroscopic world. It is one of the ways in which we relate mass and motion and force to describe the state of an object and predict its interactions with the rest of the world. As the object increases in velocity, it's energy increases and so does its mass.

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How do I calculate kinetic energy if I know the mass and velocity?

Community Answer

In classical mechanics, kinetic energy (KE) is equal to half of an object's mass (1/2*m) multiplied by the velocity squared. For example, if a an object with a mass of 10 kg (m = 10 kg) is moving at a velocity of 5 meters per second (v = 5 m/s), the kinetic energy is equal to 125 Joules, or (1/2 * 10 kg) * 5 m/s2.

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Question

How do I calculate change in kinetic energy?

Community Answer

The change in kinetic energy of the object is equal to the work done by the net force acting on it. This is a very important principle called the work-energy theorem. After you know how work relates to kinetic energy, you're ready to take a look at how kinetic energy relates to the speed and mass of the object.

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