Circular motion

An unbalanced force of 40 Newtons keeps a 5 kilogram object traveling in a circle of radius 2 meters. What is the speed of the object?

• 8 m/s

• 16 m/s

• 2 m/s

• 4 m/s

A fan spins with a constant angular speed of 500 radians/second. How long will it take to cover an angle of 2π radians (one revolution)?

• 0.013 s
• 0.002 s
• 76.9 s
• 6.28 s

A bob of mass 0.50 kg is suspended from the end of a piece of string 0.45 m long.

The bob is rotated in a vertical circle at a constant rate of 120 revolutions per minute.

What is the tension in the string when the bob is at the bottom of the circle?

• 5.8N

• 31N

• 36N

• 40N

An object of mass m is attached to a string and then whirled in a horizontal circle. The speed of the object is

slowly increased from zero. The string breaks when the object has a maximum speed of 1.00 m s−1.

The experiment is repeated with an identical string but with an object of mass 1.5 m. The radius of the circle is

kept constant.

What is the maximum speed of this object when the string breaks?

• 0.67 m s−1

• 0.82 m s−1

• 1.22 m s−1

• 1.50 m s−1

Fig shows the drum of a washing machine.

The clothes inside the drum are spun in a vertical circular motion in a clockwise direction.

The washing machine is switched off and the speed of the drum slowly decreases. The clothes at the top of the

drum at point B start to drop off at a certain speed v.

At this speed v, the normal contact force on the clothes is zero.

Calculate the speed v.

Phobos is one of the two moons orbiting Mars. Fig. 17.1 shows Phobos and Mars.

Fig. 17.1

The orbit of Phobos may be assumed to be a circle. The centre of Phobos is at a distance 9380 km from the

centre of Mars and it has an orbital speed 2.14 × 103 m s−1.

i.

On Fig. 17.1, draw an arrow to show the direction of the force which keeps Phobos in its orbit. [1]

ii. Calculate the orbital period T of Phobos.

T =.............. s

iii. Calculate the mass M of Mars.

M = ........kg