GCSE Physics- Energy & Efficiency questionWatch
-->(A car of mass 1,000 kg begins stationary on a road at the top of a mountain, at a height h = 3,000 m. The car then rolls freely down a winding road, traveling a total distance of 5 km, to reach the height h = 2,000 m. Assume g = 9.8 ms-2)
1a. How much energy did the car lose on descent? Give your answer to 3 significant figures, with units.
Ans: Energy lost = 9,800,000 J.
1b. At this point, how much energy is stored in a gravitational potential store? Give your answer in kJ.
Ans: GPE = 19,600 kJ.
1c. The car continues to roll down the mountain, where it reaches the bottom. Here the height h = 0 m. Assuming no further energy is lost and all the GPE from the top of the mountain is transformed into KE, what is the final velocity of the car? Give your answer to 3 significant figures.
Ans: Final velocity = ___ms-1
Loss in PE = Gain in KE
mgh = 1/2 mv2
gh= 1/2 v2 (upon dividing both sides by common factor m or striking it off)
9.8 X 3000 = 0.5 v2
v2 = 58800
v = 242. 49M/S
Is that it? If not, then the answer accounts for the energy loss
Hope this helps u
Seems that you have a value for the amount of GPE converted so you just have to rearrange the formula for KE
KE = 1/2 m v^2
Gravitational Potential energy= mass x gravitational filed strength x changing height.
For part a, we simply use the information given in the question.
1. Substitute the formula GPE=mgh --> GPE= 1,000kg x (3,000m-2,000m) x 9.8 ms-2= 9,800,000J
Since we figured out the energy lost in part a, to work out part b, all we need to do is find the initial energy, take the energy lost away from it and convert J to kJ.
1. Substitute the formula: GPE=mgh --> GPE= 1,000kg x 3000m x 9.8 ms-2= 29,400,000J
Notice how this time we only use the initial height, this is because we only want to know the initial energy.
2. Now find the energy left using subtraction: 29,400,000J - 9,800,000J= 19,600,000J
3. Finally, we need to convert J to kJ. This can be done by doing 19,600,000J x (1/1000)= 19,600kJ
The 1/1000 is the scale factor that converts J to kJ.