Physics 145 Module 8- Dynamics 2

A coin of mass 3.0g sits 0.30 m away from the center of a turntable where the coefficient of static friction is 0.60. If the turntable takes 3.00 s/rev, what is the static frictional force on the coin?

0.0039 N

In space, a spaceship is designed to simulate gravity by spinning. If the radius of the spaceship is 30.0 m, what angular speed is required so that someone at the edge will experience an acceleration of magnitude g?

0.57 rad/s

In a car, you're making a turn of radius of curvature R, and you're moving at speed v. Your tires are on the verge of slipping. If the radius of curvature decreases to R/3, what should you reduce your speed to in order to remain on the road? Assume that the force providing the centripetal acceleration does not depend on the speed of the car or the radius of curvature.

0.58v

What is the orbital speed for objects near the moon's surface? The radius of the moon is 1740 km, and the magnitude of the acceleration due to gravity on the surface of the moon is approximately 1/6th the magnitude on the earth's surface.

1.7 km/s

A ball is thrown as a projectile. Its initial speed is 20.0 m/s, and it is shot at an angle 60.0° above the horizontal. What is the radius of curvature of the arc at the top of the trajectory?

10.2 m

A string of length 2.0 m will break if the tension exceeds 400 N. What is the fastest speed that you could whirl a 5.0 kg object around in a circle using this string before the string breaks?

13 m/s

Your physics professor has a weight of 710 N when measured by a spring-scale at the north pole. However, the professor weighs a little less at the equator. The reason: The gravitational force (constant) needs to be a little larger that a vertically upward normal force in order to provide the net force required for circular motion. How much less does your professor weigh at the equator? Ignore any difference in the radius of the earth.

2.4 N

You're designing a Ferris wheel ride (a vertical circle). The Ferris wheel has radius 15.0 m, and you would like the Ferris wheel to go as quickly as possible (with constant speed) such that nobody feels a normal force that is more than 5% different from mg, their normal weight. What is the fastest speed this Ferris wheel can have?

2.7 m/s

The acceleration due to gravity on an asteroid is 0.042 m/s2. If the radius of the asteroid is 200.0 m, then what speed must you throw an object in order for it to orbit around the asteroid in circular motion?

2.9 m/s

A car, of total mass 1500 kg (including all occupants), moves at a constant 20.0 m/s. The car encounters a dip in the road: the dip is a section of a circle of radius 100.0 m. When the car is at the lowest point in this dip in the road, what is the normal force on the (car + occupants)?

20700 N

A banked curve is inclined at 25.0° relative to the horizontal. The radius of curvature of the circle which a car travels around (on this banked curve) is 100.0 m. What speed does the car need to move on this banked curve in order for there to be no friction acting on the car?

21.4 m/s

As part of a physics demonstration, you swing a bucket of water around in a vertical circle of radius 1.00 m. How fast must you swing the bucket in order for no water to fall out at the top of the circle?

3.1 m/s

A coin sits 0.30 m away from the center of a turntable where the coefficient of static friction is 0.60. If the turntable very slowly increases in speed, what is the angular speed of the turntable when the coin starts to slip?

4.4 rad/s

A car moves with speed 30.0 m/s along a banked curve. The radius of curvature of the circle which a car travels around (on this banked curve) is 100.0 m. At what angle should the curve be banked in order for there to be no friction acting on the car?

42.6

An object moving in nonuniform circular motion has, at one instant, a speed of 5.0 m/s and a tangential acceleration of 5.0 m/s2. What is the angle between the velocity and acceleration vectors if the radius of the circle is 5.0 m?

45

Suppose a car takes a freeway off-ramp moving at constant speed 20.0 m/s. If the radius of curvature of the circular motion is 80.0 m, what is the magnitude of the centripetal acceleration?

5.00 m/s^2

A pendulum has a mass 4.0 kg connected at the end of a 2.0-m-long string. The tension in the string when the mass is at its lowest point is 100.0 N. What is the speed of the mass at this lowest point?

5.5 m/s

A ball of mass 1.00 kg is swung at constant speed around a vertical circle of radius 0.750 m. The tension in the string used is 40.0 N when the ball is at the highest point in the trajectory. What is the tension in the string at the lowest point?

59.6 N

Suppose a car of mass 1400 kg takes a freeway off-ramp moving at constant speed 20.0 m/s. If the radius of curvature of the circular motion is 80.0 m, what is the magnitude of the radial component of the net force on the car?

7000 N

In space, a spaceship is designed to simulate gravity by spinning. If the radius of the spaceship is 30.0 m, it requires a certain angular speed so that someone at the edge of the spaceship will experience an acceleration of magnitude g. This is at the feet of someone standing at at edge of the spaceship. If the person is 1.7 m tall, what acceleration do they experience at their head?

9.2 m/s^2

A particle is moving around counterclockwise along a circle in the xy-plane centered around the origin. If the particle is speeding up, what is the direction of the net force on the particle when it is at the location (x,y)=(0,+R)(x,y)=(0,+R)? (where R is the radius of the circle.)

Down and left

If an object moves with constant speed in a circle, which of the following is true?

Neither the velocity nor the acceleration is constant.

A coin sits 0.30 m away from the center of a turntable where the coefficient of static friction is 0.60. If the turntable very slowly increases in speed, why does the coin eventually slip?

The static friction is not enough to be able to provide the required centripetal acceleration inward toward the center of the circle.

Suppose you're in the front passenger seat in a car in the U.S. (so, on the right side of the vehicle). The car makes a quick left turn. Which of the following best explains why you slam into the window?

You don't feel a force toward the window; you're moving in a straight line, and the window turns into you. It feels like there is a force to the right, but this is a consequence of you being in a noninertial frame.

A ball is swung around a horizontal circle such that the tension in the rope is both balancing the weight of the ball as well as keeping the ball moving in the circle. If the rope makes a 45° angle with respect to the vertical, what is the speed of the ball in terms of the radius of the circle R (and magnitude of the acceleration due to gravity g)?

gR−−−√