Can the KE of a car be converted into work by stopping it at 100 km/hr?

In summary, the amount of work required to stop a 1000 kg car traveling at 100 km/hr can be calculated using the formula KE=1/2mv^2, where KE is kinetic energy, m is the mass, and v is the velocity. To convert the velocity from km/hr to m/s, the conversion factor of (1000 m)/(1 km) * (1 hr)/(3600 s) can be used. The final answer for the work required is 386,000J, which can be derived by setting up the conversion correctly and solving the equation.
  • #1
rueberry
5
0
How much work is required to stop a 1000 kg car traveling at 100 km/hr?

What I was thinking was that I would use the formula for KE,
KE=1/2mv2 (last two of course is for squared
since the KE would equal work. I have gotten as far as:

KE= 1/2(1000 kg)(100km/hr)2

I am assuming that somewhere there is a conversion needed, I'm just not getting the next steps.
 
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  • #2
Which next steps? Just convert the km/hr into m/s and you're done.
 
  • #3
Then maybe I'm not setting up the conversion correctly, I was using dimensional analysis and set it up

(100 km/hr) (1000m) (3600 sec) = 3.6 x 10^8
(1 km) (1 hr)

but I know this is wrong, by the time you square it and finish the equation, its way too big. The answer in the book is 386,000J, but I keep getting answers with 360 b/c of the sec. I'm sure this is a simple mistake I'm making, but I'm still stuck. Sorry.
 
  • #4
the hour is on the bottom!
your conversion factors should be
(1000 m)/(1 km) * (1 hr)/(3600 s)

I suppose here, 100% of the Work removes KE.
 

1. What is work and energy in relation to a car?

Work and energy refer to the physical effort required to move a car from one point to another, as well as the ability of the car to do work or exert force. Work is defined as the force applied to an object multiplied by the distance it moves, while energy is the ability to do work.

2. How is work and energy related to the motion of a car?

Work and energy are closely related to the motion of a car. When an external force, such as the engine, is applied to a car, it does work on the car by moving it a certain distance. This work increases the car's kinetic energy, which is the energy associated with its motion. Similarly, when the car is braking, the work done by the brakes decreases the car's kinetic energy, eventually bringing it to a stop.

3. What factors affect the work and energy of a car?

The work and energy of a car are affected by several factors, including its mass, speed, and the external forces acting on it, such as friction and air resistance. The car's engine also plays a crucial role, as it provides the external force needed to move the car and increase its energy.

4. How is the work and energy of a car calculated?

The work done on a car can be calculated by multiplying the force applied to the car by the distance it moves. This is given by the equation W = Fd, where W is work, F is force, and d is distance. The car's energy, specifically its kinetic energy, can be calculated using the equation KE = 1/2mv^2, where m is the car's mass and v is its velocity.

5. How can the work and energy of a car be conserved?

According to the law of conservation of energy, energy cannot be created or destroyed, only transferred from one form to another. In the case of a car, the potential energy stored in the fuel is converted into kinetic energy to move the car. To conserve the car's energy, it is important to maintain it properly and use efficient driving techniques, such as avoiding sudden accelerations and braking, which can waste energy. Additionally, using alternative energy sources, such as electric cars, can also help conserve energy and reduce the car's impact on the environment.

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