Homework Help: Physics

Posted by Sara on Saturday, October 27, 2012 at 4:44pm.

A car of mass 1100 kg starts from rest at sea level and climbs 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 the hill the driver turns off the
engine and coasts down to an altitude of 15 m. Assume the friction and the air resistance to be
negligibly small.
A. What is the speed of the car when the altitude is 15m?
B. ) 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 _____?

Physics - Damon, Saturday, October 27, 2012 at 5:28pm
mass is irrelevant - cancels everywhere

Energy at top = m g h + (1/2) m v^2
= (9.8 * 50 + 625/2)m
= 803 m Joules

Energy at 15 = m ( 9.8*15 + v^2/2) = 803 m

v^2/2 = 656

v = 36.2 m/s

coasting up fro 15, still same total energy
m g h =803 m
9.8 h = 803
h = 81.9 meters
Physics - Sara, Saturday, October 27, 2012 at 7:00pm
Thanks!!

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