Exam 6: Force and Motion

One end of a 1.0-m long string is fixed; the other end is attached to a 2.0-kg stone.The stone swings in a vertical circle, passing the bottom point at 4.0 m/s.The tension force of the string at this point is about:

Uniform circular motion is the direct consequence of:

If a satellite moves above the Earth's atmosphere in a circular orbit with constant speed, then:

A car is traveling at 15 m/s on a horizontal road.The brakes are applied and the car skids to a stop in 4.0 s.The coefficient of kinetic friction between the tires and road is:

The same heavy wooden block is dragged by a force along a rough steel plate, as shown below for two possible situations.The magnitude of the acceleration is the same for the two situations; do not assume that the magnitude of is the same.The magnitude of the frictional force in (ii), as compared with that in (i)is:

A giant wheel, 40 m in diameter, is fitted with a cage and platform on which a man can stand.The wheel rotates at such a speed that when the cage is at X (as shown)the force exerted by the man on the platform is equal to his weight.The speed of the man is:

An 800-N passenger in a car presses against the car door with a 200 N force when the car makes a left turn at 13 m/s.The (faulty)door will pop open under a force of 800 N.Of the following, the least speed for which the man is thrown out of the car is:

A 5.0-kg crate is resting on a horizontal plank.The coefficient of static friction is 0.50 and the coefficient of kinetic friction is 0.40.After one end of the plank is raised so the plank makes an angle of 30° with the horizontal, the force of friction is:

The iron ball shown is being swung in a vertical circle at the end of a 0.7-m string.How slowly can the ball go through its top position without having the string go slack?

A ball is thrown upward into the air with a speed that is greater than terminal speed.On the way up it slows down and, after its speed equals the terminal speed but before it gets to the top of its trajectory:

One end of a 1.0-m string is fixed; the other end is attached to a 2.0-kg stone.The stone swings in a vertical circle, passing the top point at 4.0 m/s.The tension force of the string at this point is about:

Why do raindrops fall with constant speed during the later stages of their descent?

The system shown remains at rest.The force of friction on the block on the slope is:

An object moves in a circle.If the mass is tripled, the speed halved and the radius unchanged then the magnitude of the centripetal force must be multiplied by a factor of:

A cube has a drag coefficient of 0.8.What would be the terminal velocity of a sugar cube 1 cm on a side in air (ρ = 1.2 kg/m³)? Take the density of sugar to be 1.6 x 10³ kg/m³.

An object moves around a circle.If the radius is doubled keeping the speed the same then the magnitude of the centripetal force must be:

A 12-kg crate rests on a horizontal surface and a boy pulls on it with a force that is 30° below the horizontal.If the coefficient of static friction is 0.40, the minimum magnitude force he needs to start the crate moving is:

A 5.0-kg crate is resting on a horizontal plank.The coefficient of static friction is 0.50 and the coefficient of kinetic friction is 0.40.After one end of the plank is raised so the plank makes an angle of 25°with the horizontal, the force of friction is:

A professor holds an eraser against a vertical chalkboard by pushing horizontally on it.She pushes with a force that is much greater than is required to hold the eraser.The force of friction exerted by the board on the eraser increases if she:

When the brakes of an automobile are applied, the road exerts the greatest retarding force: