Homework help: Work and Energy, Free fall

In summary: So, the answer should not have more than 1 significant digits, too.In summary, the 200 kg object falling from 20 m to 5 m with an initial velocity of 10 m/s has a new speed of approximately 20 m/s, using the equation vf²=vi²+2ad. Using the conservation of energy method also yields the same result. The distance for the new speed is 15 m, and 9.8 can be used for the acceleration as it is in freefall. However, the final answer should be rounded to 1 significant digit to match the given values.
  • #1
Syeda
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0

Homework Statement


A 200 kg object moves at 10 m/s at 20m (vertically). It falls to a height of 5 m. Find the new speed.

Homework Equations


vf²=vi²+2ad

The Attempt at a Solution


vf²=(10m/s)²+2(9.8m/s²)(15m)
vf=19.8m/s

To find the distance for the new speed I did 20-5, but I'm not sure it's correct.
Also I'm not sure if I'm supposed to use 9.8 for the acceleration
 
Last edited:
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  • #2
Use energy conservation.

On edit: I noticed that you have posted two different threads with the same title. Please try to avoid this because it can be confusing.
 
  • #3
"moves at 10m/s" in which direction? Vertically? Horizontally?
 
  • #4
CWatters said:
"moves at 10m/s" in which direction? Vertically? Horizontally?
Vertically, from 20 m to 5 m
 
  • #5
Then I believe your working in #1 is correct.

You could use conservation of energy method to check you get same answer if you want.

Edit: I just noticed the title says work and energy so perhaps your tutor intended you to use conservation of energy method rather than the equations of motion.
 
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  • #6
CWatters said:
I just noticed the title says work and energy so perhaps your tutor intended you to use conservation of energy method rather than the equations of motion.
Arguably, OP's relevant equation, vf²=vi²+2ad is the energy conservation equation with a factor of (½)m multiplying both sides canceled out.
 
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  • #7
Everything you have done in step #3 is correct.
Yes, it moves 15 metres.
Yes, it is freefall, so you can use 9.8 for the acceleration.
Remember that if the solution has to be in proper significant digits, you will need to round it to 1 digit because the lowest number of significant digits in your original given values is 1 digit. In fact, ALL of the given numbers are 1 significant digit long.
 
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Related to Homework help: Work and Energy, Free fall

1. What is work in terms of physics?

Work in physics is defined as the product of force and displacement in the direction of the force. It is measured in joules (J) and is a measure of the energy transferred to an object by a force.

2. How is work calculated?

Work is calculated by multiplying the magnitude of the force applied to an object by the distance the object moves in the direction of the force. Mathematically, it can be represented as W = F*d, where W is work, F is force, and d is displacement.

3. What is energy in physics?

In physics, energy is defined as the ability to do work. It is a scalar quantity and is measured in joules (J). There are various forms of energy, including kinetic, potential, thermal, and chemical energy.

4. How is free fall defined?

Free fall is the motion of an object under the influence of gravity alone. This means that the object is not being supported by any other forces and is only subject to the force of gravity. In a vacuum, all objects will fall with the same acceleration due to gravity, regardless of their mass.

5. How is free fall related to work and energy?

In free fall, the object is only subject to the force of gravity, so the work done on the object is equal to the change in its potential energy. As the object falls, its potential energy decreases and its kinetic energy increases. This relationship between work, energy, and free fall is described by the equation W = ∆PE = ∆KE.

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