http://www.ck12.org Chapter 5. Centripetal Forces
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- A 700kg car makes a turn going at 30 m/s with radius of curvature of 120m. What is the force of friction
between the car’s tires and the road? - An object of mass 10 kg is in a circular orbit of radius 10 m at a velocity of 10 m/s.
a. Calculate the centripetal force (inN) required to maintain this orbit.
b. What is the acceleration of this object? - Suppose you are spinning a child around in a circle by her arms. The radius of her orbit around you is 1 meter.
Her speed is 1 m/s. Her mass is 25 kg.
a. What is the magnitude and direction of tension in your arms?
b. In her arms? - A racecar is traveling at a speed of 80.0 m/s on a circular racetrack of radius 450 m.
a. What is its centripetal acceleration in m/s^2?
b. What is the centripetal force on the racecar if its mass is 500 kg?
c. What provides the necessary centripetal force in this case? - The radius of the Earth is 6380 km. Calculate the velocity of a person standing at the equator due to the
Earth’s 24 hour rotation. Calculate the centripetal acceleration of this person and express it as a fraction of the
acceleration g due to gravity. Is there any danger of “flying off”? - Neutron stars are the corpses of stars left over after supernova explosions. They are the size of a small city,
but can spin several times per second. (Try to imagine this in your head.) Consider a neutron star of radius
10 km that spins with a period of 0.8 seconds. Imagine a person is standing at the equator of this neutron star.
a. Calculate the centripetal acceleration of this person and express it as a multiple of the accelerationgdue
to gravity (on Earth).
b. Now, find the minimum acceleration due to gravity that the neutron star must have in order to keep the
person from flying off.
Answers to Selected Problems
- 5250 N
- a. 100 N b. 10 m/s^2
- a. 25 N towards her b. 25 N towards you
- a. 14.2 m/s^2 b. 7. 1 × 103 N c. friction between the tires and the road
5..0034g - a. 6. 3 × 104 gm/s^2 b. The same as a.
Summary
In this chapter students will learn about circular motion, centripetal acceleration and how to think about and solve
problems on centripetal forces and motion.