Concept explainers
Consider a 2100-kg car cruising at constant speed of 70 km/h. Now the car starts to pass another car by accelerating to 110 km/h in 5 s. Determine the additional power needed to achieve this acceleration. What would your answer be if the total mass of the car were only 700 kg?
The additional power needed to achieve the acceleration.
If the total mass of the car is 700 kg, what would be the answer in order to achieve the acceleration?
Answer to Problem 50P
The additional power needed to achieve the acceleration is
If the total mass of the car is 700 kg, the answer in order to achieve the acceleration is
Explanation of Solution
Write the energy balance equation for a control volume when car cruising is taken as the system.
Here, the rate of energy transfer entering and leaving the system is
Since no energy is leaving the room,
Substitute 0 for
Here, the change in the internal energy of the system is
Rewrite Equation (II) when rate of work done on the system.
Here, velocity at inlet and outlet is
If the total mass of the car is 700 kg, calculate the additional power needed to achieve the acceleration.
Conclusion:
Substitute 2100 kg for m, 110 km/h for
Thus, the additional power needed to achieve the acceleration is
Substitute 700 kg for m, 110 km/h for
Thus, if the total mass of the car is 700 kg, the answer in order to achieve the acceleration is
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