Physics1201Q Final Exam Questions
1. A man stands on a platform that is equipped with rollers. The man holds a rifle aimed horizontally, with the rifle
butt braced against the man’s shoulder. The man and the platform are both motionless. As part of a ballistics
test, the man then fires the rifle so that the bullet travels horizontally in one direction and the man and platform
move in the opposite direction to the bullet. Immediately after the bullet leaves the gun, the man and rolling
platform have kinetic energy KE1 and the bullet has kinetic energy KE2. The bullet has mass m and the man plus
platform have mass M. Find the ratio R, as given by R = (KE2 / KE1) in terms of M and m.
2. A box is placed on the outer rim of a horizontal disk that has an axle through its center. The disk is set to be
spinning at constant angular speed with a period of 24 seconds. The radius of the disk is 4.6 m. How large must
the coefficient of static friction be between the box and the disk for the box to stay on the rotating disk without
slipping?
3. An oil drilling machine rests on the ocean floor about 5000 ft below the ocean surface. It drills
through an additional 13,000 feet of soil when there is a failure and oil escapes through some
kind of rupture. Assume the drill hole has a circular base consisting of the drill extending
through a tall column of muddy paste, and that the diameter of this circular base is 18 cm.(a)
Compute the approximate hydrostatic pressure at the base of the drill hole just before the
failure. Assume the density of water is 1000 kg/m
3
and the density of the soil is 2.5 times that
of water. (b) What would be the force on the circular base of the drill hole at this pressure?
4. Lake Champlain has a surface area of 1,126 km
2
. It freezes in the winter with an average ice thickness of 0.5 m.
(a) What total energy does it take to melt the ice once spring comes? (b) If this energy is provided by sunlight
shining on the lake at 200 W/m
2
, and this energy is only half absorbed, how long will it take the ice on the lake
to melt?
5. A geosynchronous satellite stays above the same point on the equator as the earth revolves. Given the mass of
the earth M, and gravitational constant G, find the distance D of the satellite from the earth’s center.
6. An oil spill on the ocean is sometimes modeled as having a velocity that has two components: a wind induced
velocity that is 3% of the true wind velocity and an independent tidal velocity Vtidal. The tidal velocity is 3.0 km/hr
due north and V wind = 40 km/hr 20 degrees north of east. In six hours, how far is the oil predicted to move in the
northerly direction?
7. The above diagram illustrates the simple mass on a spring accelerometer. Note that were the acceleration to the
right, instead of the left, the spring would compress rather than stretch. Let there be a vehicle with a flat top on
which such an accelerator is fastened. The vehicle moves horizontally at all times and the accelerometer is also
mounted horizontally as shown above. The mass on the spring is m, the spring constant is K, and the mass of the
vehicle is M, where M >> m. The length of the unstretched spring is D, and the vehicle is moving at constant
velocity to the west. Gradually the brakes are applied, and then held at constant braking force. The length of the
spring is now observed to be L = D – b where L, D, and b are all positive numbers. What is the braking force on
the vehicle in terms of given quantities?
8. For the regenerative braking system of a train, a cylindrical spinning flywheel is used to store energy. One train
has a flywheel of mass 3000 kg, a diameter of 0.5 m, and attains an angular velocity of 8,000 RPM. If ten gallons
of gasoline store 140 kw h of energy, how many gallons of gasoline are equivalent to the fully spinning flywheel
in terms of energy storage?

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