1. A car of mass 1100 kg starts from rest at sea level andclimbs a hill of altit

Question

1. A car of mass 1100 kg starts from rest at sea level andclimbs a hill of altitude 50 m. At the
top of the hill the car has a speed of 25 m/s. From the top of thehill the driver turns off the
engine and coasts down to an altitude of 15 m. Assume the frictionand the air resistance to be
negligibly small. (6 points each, no partial credit;use the back of any page or any space on this
page for scratch work, but these will not be graded)

a) The work produced by the engine of the car is ____882750____Joule. (correct)


b) The speed of the car when the altitude is 15mis _36.21_ m/s

c) After passing the altitude of 15m, the driver climbs up again,without turning the engine on. In
this case, the speed of the car would be zero

at an altitude of ___81.9___ m. (correct,using correct B answer)

I don't know how to get answer D

d) In reality the friction and the air resistance are not zero. Ifthe work needed to overcome the
friction and the air resistance is5.2x10^5 Joules, the answerto part (a) would change. In this
case, the work produced by the engine to climb to 50 m and have aspeed of 25 m/s at the top I don't

Explanation / Answer

a) work done = gain in KE +PE = 1/2*m*v^2 + mgh=1/2*1100*25*25 + 1100*9.8*50 =882,750 joules b) change in PE = gain in KE mg(H-h)=1/2mv^2 - 1/2*m*v'^2 g(50-15)=1/2 *v^2 -1/2*25*25 v=36.2077 m/s c) 1/2*m*v^2 = mgh 1/2*36.21*36.21=9.8*h h=66.89 m total altitude = 15+66.89 = 81.9 m d) yes it will change 5.2x10^5 Joules + 882 750 joules=1402750 joules

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