Question

1. a mechanic is using a wrench to loosen a nut on a bolt. the nut isn't moving. describe two ways she can increase the torque on wrench

2. What is the relationship between the net torque applied to an object and the objects rotational motion?

3. A 55kg person riding a bike puts all her weight on each pedal when climbing a hill. The pedals rotate in a circle of radius 17 cm.

a) what is the maximum torque she exerts?

b) at what point during the rotation of the pedals does she exert the greatest torque?

5) a person exerts a force of 55 N on the end of a door 74 cm wide. What is the magnitude of the torque if the force is exerted

a) perpendicular to the door, and

b) at a 45 degrees angle to the face of the door>

6) Calculate the net torque about the axle of the wheel. F1= 45N and acts at a distance r1=0.32 m from the axle, while F2= 38 N and acts at a distance r2= 0.48 m from the axle at the angle 30 degrees. What is the direction of the torque?

7) what is the second law of motion for rotation? What is moment of inertia

8) Calculate the moment of inertia of a bicycle wheel 66.7 cm in diameter. The rim and tire have a combined mass of 1.25kg. Why can the mass of the hub be ignored?

9) a band leader is twirling a baton about its center. What torque is required to angularly accelerate the baton from rest to 25 rad/s in 0.75s? Assume the baton is two 120 g masses connected by a 0.74 m massless rod

10) a softball player swings a bat, accelerating it from rest a 3.0 rev/s in a time of 0.20s. Approximate the bat as a 2.2kg uniform rod of length 0.95m, and compute the torque the player applies to one end of it.

Answer 1

1. Magnitude of torque is given by the formula:

Where r is the magnitude of position vector of the point of application w.r.t. nut and bolt. F is the magnitude of force applied and is the angle between the line of action of force and wrench.

She can increase the torque by:

i) By increasing 'r' i.e. the distance of point of application of force from the location of nut.

ii) By making the force perpendicular to the Wrench i.e. by making = 90^o.

2. Angular acceleration '' produced in an object is directly proportional to the net torque '' applied if it moment of inertia 'I' is constant about the given axis and the relation between them is:

Where I = Moment of inertia of the object about the given axis.

3. Mass of the person, m = 55 kg

Radius of the circle in which pedals rotate, r = 17 cm = 0.17 m

a) Maximum torque that she applies while climbing the hill is:

b) She exerts the maximum torque on the pedals, when the pedals are horizontal because at that time angle between radius vector and force is 90^o.

5. Force applied, F = 55 N

distance of force from the axis, r = 74 cm = 0.74 m

a) If fore is applied perpendicular to the door, thee torque is:

b) If force is applied at 45^o to the door, then torque is: