Other Physics Answers

A disc of mass 16kg and radius 0.25m acquires an angular velocity of 126 rad/s in 8.0

seconds from rest. If the disc rotates about an axis through centre of the disc and in a

plane perpendicular to the disc, find the torque responsible for the rotation.

What is the rotational kinetic energy of a 60cm diameter bicycle wheel of mass 4.0kg

when the bicycle is travelling at 4.0m/s. Take the radius of gyration k = 50?

1,A motorist is making a vertical loop inside a ‘death well’. What is the minimum speed

required to perform a vertical loop if the radius of the chamber is 25 m?

2. The earth is assumed to be sphere of radius 6.37 x 106m. if a body of mass m is on the

surface of the earth, calculate the mass of the earth.

3. A 70 kg man stands in contact against the wall of a cylindrical drum of radius 3m rotating

about its vertical axis. The coefficient of friction between the wall and his clothing is 0.15.

What is the minimum rotational speed of the cylinder to enable the man to remain stuck to

the wall, when the floor is suddenly removed?

4. A circular race track of radius 500 m is banked at an angle of 200. Calculate the maximum

permissible speed to avoid slipping if

(a) there is no friction between the tires and the road.

(b) the coefficient of friction between the tires and the road is 0.15.

1.A cyclist negotiates a curve of radius 100m with a velocity 10 m/s. How much should he

lean from the vertical in doing so?

2.. A disc revolves in a horizontal plane at a steady rate of 3 revs/s. A coin will remain on the

disc if it is kept a distance of 2 cm from the axis of rotation. What is the coefficient of

friction between the coin and the disc?

1.Earth revolves around the sun with a speed of 30 km/s in an approximate circular path.

How much acceleration does it have directed towards the sun? Orbital radius of the earth

is 1.5 108 km.

2. An aircraft executes a horizontal loop at a speed of 720 km/h with its wings banked at 15o.

What is the radius of the loop?

3. A car of mass M experiences a maximum frictional force of 0.65Mg pavement as it goes

around the curved road of radius 150m. How fast can the car be moving to successfully go

around the curve?

1.A car moving at speed of 25m/s can go around a curve of 80m radius without skidding

away if the road is unbanked. Determine the coefficient of static friction between the road

and tires that would ensure the car not skid.

2. A grasshopper of mass 200g sits 20cm from the centre of a blade of a ceiling fan rotating

at 35rev/min.

(a) Determine the size of the centripetal force on a grasshopper.

(b) Calculate the value of static friction between the fly and the blade required to prevent

a grasshopper from sliding off.

1.A cyclist is riding with a speed of 27 km/h. As he approaches a circular turn on the road of

radius 80 m, he applies brakes and reduces his speed at the rate of 0.5 m/s2. What is the

magnitude and direction of the resultant acceleration of the cyclist on the circular turn?

2. A rider of a bicycle goes around a circular path of radius 50m at 15m/s. the mass of the

rider is 60kg and that of a bicycle is 25kg,

(a) What is the centripetal force keeping the bicycle going around the circular path?

(b) Calculate the normal force acting on the bicycle.

(c) What is the coefficient of friction which the bicycle tires experiences with road?

A cyclist is riding at a speed v on the level road. As he reaches a sharp circular corner of

radius r, he maintains the same speed. If the coefficient of friction between the tires and

the road is µ

(a) Show that the maximum permissible speed of the cyclist is

𝒗 = √𝝁𝒓𝒈

(b) If the cyclist’s speed was 20km/h, radius of the circular corner 15m and coefficient of

friction 0.35, show that the cyclist will skid away.

A bicycle wheel of diameter 80cm accelerates uniformly from rest to angular speed of

50rad/s in 20s.

(a) Find the angular acceleration of a wheel.

(b) If a small stone is stack between the grooves of a wheel, find its tangential and radial

acceleration.

(c) During this time, how many revolutions has this wheel turned?

(d) If the wheel turns through 250rev in coming to rest, at what rate was the angular velocity

changing?

1.A circular race track of radius 500m is banked at angle of 15o. Calculate the maximum

permissible speed to avoid slipping if

(a) there is no friction between the tires and the road.

(b) the coefficient of friction between the tires and the road is 0.3.

2. A stone is attached to the end of a rope of length l = 25 cm, and rotates the stone at a

constant speed in a circular path. If the period of rotation is 5.0s, find the stone’s centripetal

acceleration.