(a) How high a hill can a car coast up (engine disengaged) if friction is negligible and its initial speed is 96.0 km/h?
m
(b) If, in actuality, a 750 kg car with an initial speed of 96.0 km/h is observed to coast up a hill to a height 19.0 m above its starting point, how much thermal energy was generated by friction?
I CANT FIGURE OUT THIS ANSWER (PART B) . PLEASE HELP _________J
(c) What is the average force of friction if the hill has a slope 2.5° above the horizontal? (Explicitly show on paper how you follow the steps in the Problem-Solving Strategy for energy found on pages 159 and 160. Your instructor may ask you to turn in this work.)
N (down the slope)
If you move your eyes straight to the bottom you will see that I am not comfortable with what I have done!
So you should probably wait for someone else.
For part A
You would need to know the angle incline of the slope.
Because you need to have the vertical component of the initial velocity
and that would be 96sin(angle)
I suppose that you would use 2.5 degrees
Vy=96sin(2.50)≈4.187461187km/hour
4.187461187×1000(60×60)=1.1631836630555556
approx vertical velocity is 1.1632 m/s Initially u=1.1632
a = -9.8m/s^2
Find height (s) when velocity = 0 v=0
Number 4 has u, a, v, and s so use that one
v2=u2+2as0=1.163182+2∗−9.8∗s
0=1.163182+2×−(9.8×s)⇒s=1146030451660192226⇒s=0.0690299853265305
This is the vertical height that it will coast in metres.
Draw the triangle and you can work out the distance it will coast up the hill
0.069sin360∘(2.5∘)=1.5818654082098661
1.58 metres - That does not look right
HELP - What did I do wrong ??
»You would need to know the angle incline of the slope
Not when the question asks merely how high the hill
All the car's KE is converted to gravitational potential energy
½mv² = mgh
∴ h = ½v² ÷ g
DONE
part (b)
It doesn't gain as much gravitational PE as it would if losses were absent
so friction losses = mghideal - mghactual
Thanks you anon
ok so
96km/hour
96×1000(60×60)=803=26.6666666666666667
KEnergy=gravitationalPotentialenergy0.5mv2=mghh=0.5v2/gh=0.5∗(26.˙6)2/9.8mh=0.5∗711.111/9.8mh≈36.28m
Is this correct? It does sound better.
If this one is correct then what was wrong with my logic the first time?
Melody, your initial logic (the use of v2 = u2 + 2as) would work if you imagine the car going straight up:
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