PH8151 ENGINEERING PHYSICS (UNIT 1)

25 flashcards · Physics · by Sathyaraj Duraisamy

A gun fires a bullet of mass 50g with a velocity of 30m/s. Because of this, the gun is pushed back with a velocity of 1m/s. The mass of the gun is?
By conservation of momentum, MV = mv M = mv/V = 1.5kg.
If there is a change of angular momentum from J to 4J in 4s, then the torque is ___________
τ=dL/dt; τ=(4J-J)/4=3/4 J.
Which of the following can execute both translational and rotational motion under the influence of the external field?
A rigid body is one for which the distance between different particles does not change, even though they move. Under the influence of an external force, a rigid body can execute rotational and translational motion.
When a rope is pulled on either side, what is the stress acting on it?
A tensile stress occurs when something is being pulled. A rope experiences tensile stress because it is flexible. In other words, a rope cannot be pushed.
Fluids cannot resist sheer stress.
Fluids cannot resist sheer stress because they do not deform. Rather they flow. Fluids are opaque to transverse waves therefore they have the inability to undergo sheering stress.
A pendulum A oscillating continuously comes to rest after some time. Now make both pendulums A and B to oscillate simultaneously. What will happen?
A comes to rest earlier than B. If a body is subjected to stress or strain continuously if becomes weak due to elastic fatigue.
A copper wire of length 3m and 1mm diameter is subjected to a tension of 5N. Calculate the elongation produced, if the young’s modulus of copper is 120GPa.
Young’s modulus = (Force×Length)/(Area×Elongation); Area=πr2 Elongation = (Force ×Length)/(Area ×Young’s modulus) Elongation = 15.9mm.
Calculate the Young’s modulus in the cantilever depression method. The length is 1m which is suspended with a load of 150gm. The depression is found to be 4cm. The thickness of the beam is 5mm and breadth is 3cm.
Y = (4gl3)/(bd2 ) × M/y Y = 3.92 × 1010 N/m2.
What is the effect of annealing on elasticity of materials?
Annealing is the process of heating a material and then gradually cooling it. While annealing, constituent crystals are uniformly oriented and form larger crystal grains, which results in a decrease in their elastic properties.
Which type of elasticity is involved in tangential push on the upper face of a block?
Rigidity modulus is defined as the ratio between tangential stress and shearing strain. When a tangential stress is applied to the upper face of a block, the cube gets deformed and there is relative displacement.
A thick wire is suspended from a rigid support and no load is attached to its free end but the wire is under stress.
True The wire is maybe suspended with no load but the wire will experience some stress due to its own weight. Therefore the answer is true.
Air is more elastic than water.
False Air can be compressed easily while water is incompressible and bulk modulus is reciprocal of compressibility. Therefore, water is more elastic than air.
According to Hooke’s law of elasticity, if stress is increased, the ratio of stress to strain?
Remains Constant. According to Hooke’s law, Stress/Strain=constant.
The breaking stress of a wire depends upon ___________
The stress at which rupture of the wire occurs is called its breaking stress. Its value depends on the material of the wire.
Which of the following affects the elasticity of a substance? a) Hammering and annealing b) Change in temperature c) Impurity in substance d) All of the mentioned
All the above. All the factors change in temperature, hammering and annealing and impurity in substance affects the elasticity of a substance.
The diameter of brass rod is 4mm. Young’s modulus of brass is 9×109 N/m2. The force required to stretch 0.1% of its length is ___________
∆l/l=0.1/100 F=YA∆l/l=(Y×πr2×∆l)/l= (9×109×π×(2×10(-3))2×0.1)/100 N=360πN.
A substance breaks down by a stress of (106 N)/m2. If the density of the material of the wire is 3×(103) kg/m3, then the length of the wire of the substance which will break under its own weight when suspended vertically will be ___________
Breaking stress = mg/area=Alρg/A=lρg l=Stress/ρg=106/(3×103×10)=33.3m.
A stretched rubber has ___________
The work done in stretching the rubber is stored as its potential energy.
If in a wire of Young’s modulus Y, longitudinal strain is produced, then the value of potential energy stored in its unit volume will be ___________
Potential energy stored per unit volume, u=1/2×Stress×Strain=1/2 (Y×Strain)×Strain u=0.5YX2.
Two wires have the same material and have the same volume. However wire 1 had cross sectional area A and wire 2 has cross sectional area 3A. If the length of wire 1 increases by ∆x on applying force F, how much force is needed to stretch wire 2 by the same amount?
Y=F/A l/∆l=F/A2 Al/∆x=FV/(A2 ∆x) F=Y∆x/V A2 :FαA2 :F‘=(3A)2 :F‘/F=9 :F‘=9F.
Amorphous solids are true solids.
False Amorphous solids have disordered arrangement of atoms or molecules. The molecules of the liquid are free to move but the molecules of an amorphous solid are almost fixed at their positions. That is why we say amorphous solids are super-cooled liquids of high velocity.
An example of a perfectly plastic body is ___________ a) Quartz b) Crystal c) Putty d) Rubber
If on the removal of deforming force, a body does not regain its original configuration even a little, then it is said to be a perfectly plastic body. This putty is a perfectly plastic body.
No material is perfectly elastic.
True All materials undergo a change in their original state, howsoever small it may be, after the removal of deforming force. Hence, there is no such material that is perfectly elastic.
A body of weight mg is hanging on a string that extends in length by l. The work done in extending the string is ___________
=Average force × extension W=1/2 F×l=1/2 mg×l=mgl/2.
A given quantity if an ideal gas is at pressure P and absolute temperature T. What is the isothermal bulk modulus of the gas?
Isothermal bulk modulus of a gas = Pressure of the gas = P.