PHY for ENG 2 Flashcards by Dave Molina

Two objects move toward each other,
collide, and separate. If there was no net external force acting on the objects, but some kinetic energy was lost, then:

A. the collision was elastic and total linear
momentum was not conserved
B. the collision was not elastic and total
linear momentum was not conserved
C. the collision was elastic and total linear
momentum was conserved
D. the collision was not elastic and total
linear momentum was conserved

D. the collision was not elastic and total
linear momentum was conserved

Total linear momentum is conserved in a collision during which the net external force is zero. If kinetic energy is lost,
then by definition, the collision is not
elastic.

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When a body moves with a constant
speed along a circle

A. no work is done on it
B. no acceleration is produced in it
C. no force acts on it
D. its velocity remains constant

A. no work is done on it

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The coefficient of restitution e for a
perfectly elastic collision is:

A. -1
B. 0
C. 1
D. Infinity

C. 1

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A drum of radius R and mass M, rolls
down without slipping along an inclined
plane of angle 0. The frictional force:

A. Decreases the rotational motion
B. Decreases the rotational and translational
motion
C. Dissipates energy as heat
D. Converts translational energy to
rotational energy

D. Converts translational energy to
rotational energy

Solution: Net work done by frictional force when drum
rolls down without slipping is zero.
Wre=0

(P4Eng2 FIGURE)

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A wooden block of mass M is moving at
speed V in a straight line. How fast
would the bullet of mass m need to
travel to stop the block (assuming that
the bullet became embedded inside)?

A. MV/m
B. mV/(m+M)
C. mV/M
D. MV/(m+M)

A. MV/m

(P4Eng2 FIGURE)

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Which of the following best describes a
perfectly inelastic collision free of
external forces?

A. Kinetic energy is sometimes conserved
B. Total linear momentum is never
conserved
C. Total linear momentum is sometimes
conserved.
D. Kinetic energy is never conserved.

D. Kinetic energy is never conserved.

In a perfectly inelastic collision, kinetic energy is never conserved; some of the initial kinetic energy is always lost to
heat and some is converted to potential
energy in the deformed shapes of the
objects as they lock together.

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A solid cylinder of mass m and radius R rolls down an inclined plane of height h without slipping. The speed of its centre of mass when it reaches the bottom is:

A. √(4gh/3)
B. √(4g/h)
C. √(2gh)
D. √(3gh/4)

A. √(4gh/3)

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The vector sum of two forces is
perpendicular to their vector
differences. In that case, the forces

A. are equal to each other
B. are equal to each other in magnitude
C. cannot be predicted
D. are not equal to each other in magnitude

B. are equal to each other in magnitude

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A particle of mass m is projected with velocity v making an angle of 45° with the horizontal. When the particle lands on the level ground the magnitude of the change in its momentum will be:

A. 2mv
B. zero
C. mv√(2)
D. mv/√(2)

C. mv√(2)

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For a satellite moving in an orbit around the earth, the ratio of kinetic energy to potential energy is:

A. 1/2
B. 1/√(2)
C. 2
D. √(2)

A. 1/2

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Two projectiles are fired from the same point with the same speed at angles of projection 60° and 30° respectively.
Which one of the following is true?

A. Their landing velocity will be same
B. Their range will be same
C. Their time of flight will be same
D. Their maximum height will be same

B. Their range will be same

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Assuming a frictionless, massless
pulley, determine the acceleration of the
blocks once they are released from rest.

(P4Eng2 FIGURE)

A. (M-m)g/(M+m)
B. Mg/(m+M)
C. (M+m)g/(M-m)
D. Mg/m

A. (M-m)g/(M+m)

FT -mg=ma(1)
FT -Mg= M(-a)(2)
a=Mg-mg/M+m=M-mg/M+m

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The coefficient of static friction
between a box and a ramp is 0.5. The ramp’s incline angle is 30°. If the box is placed at rest on the ramp, the box will do which of the following?

A. Move with constant velocity down the
ramp.
B. Not move.
C. Accelerate briefly down the ramp but then
slow down and stop.
D. Accelerate down the ramp.

D. Accelerate down the ramp.

The force pulling the block down the
ramp is mg sin 0, and the maximum
force of static friction is μsFN = smg cos e. If mg sin θ is greater than usmg cos 0, then there is a net force down the
ramp, and the block will accelerate
down. So, the question becomes,”Is
sin θ greater than μs cos θ?” Since θ=
30° and ps = 0.5, the answer is “yes.”

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The average speed of a moving object
during a given interval of time is always.

A. the magnitude of its average velocity over
the interval
B. its acceleration multiplied by the time
interval
C. one-half its speed at the end of the interval
D. the distance covered during the time
interval divided by the time interval

D. the distance covered during the time
interval divided by the time interval

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A ball is in free fall. Its acceleration is:

A. downward during both ascent and
descent
B. downward during ascent and upward
during descent
C. upward during ascent and downward
during descent
D. upward during both ascent and descent

A. downward during both ascent and
descent

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Which of the following is NOT an
example of accelerated motion?

A. Vertical component of projectile motion
B. Horizontal component of projectile
motion
C. Earth’s motion about sun
D. Circular motion at constant speed

B. Horizontal component of projectile
motion

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A bullet shot horizontally from a gun:

A. strikes the ground much later than one
dropped vertically from the same point at
the same instant
B. travels in a straight line
C. never strikes the ground
D. strikes the ground at approximately the
same time as one dropped vertically
from the same point at the same
instant

D. strikes the ground at approximately the
same time as one dropped vertically
from the same point at the same
instant

Three blocks (A,B,C), each having mass
M, are connected by strings as shown.
Block C is pulled to the right by a force F
that causes the entire system to
accelerate. Neglecting friction, the net
force acting on block B is:

A. F/2
B. Zero
C. 2F/3
D. F/3

D. F/3

(P4Eng2 FIGURE)

A brick slides on a horizontal surface.
Which of the following will increase the
magnitude of the frictional force on it?

A. Putting a second brick on top
B. Decreasing the surface area of contact
C. Increasing the surface area of contact
D. Decreasing the mass of the brick

A. Putting a second brick on top

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

A. The force of gravity is negligible for
objects as small as raindrops
B. The gravitational force is the same for all
drops
C. Air resistance just balances the force of
gravity
D. The drops all fall from the same height

C. Air resistance just balances the force of
gravity

The amount of work required to stop a
moving object is equal to:

A. the mass of the object times its velocity
B. the kinetic energy of the object
C. the mass of the object times its
acceleration
D. the velocity of the object

B. the kinetic energy of the object

Momentum may be expressed in:

A. Kg/m
B. N-s
C. gram-s
D. kg/(m-s)

B. N-s

The momentum of an object at a given
instant is independent of its:

A. Speed
B. Acceleration
C. Velocity
D. Mass

B. Acceleration

Two objects, P and Q, have the same
momentum. Q has more kinetic energy
than P if it:

A. is moving slower than P
B. weighs the same as P
C. weighs more than P
D. is moving faster than P

D. is moving faster than P

If the total momentum of a system is changing: A. the system must be under the influence of gravity B. the center of mass must have constant velocity C. particles of the system must be exerting forces on each other D. a net external force must be acting on the system

D. a net external force must be acting on the system

Force: A. equals the negative integral (with respect to distance) of the potential energy function B. equals the time rate of change of momentum C. is the ability to do work D. is the rate of change of doing work

B. equals the time rate of change of momentum

The physical quantity "impulse" has the same dimensions as that of: A. Energy B. Power C. Momentum D. Force

C. Momentum

Which is the correct statement about law of polygon of forces? A. if any number of forces acting at a point can be represented in direction and magnitude by the sides of a polygon taken in order, then the forces are in equilibrium B. if any number of forces acting at a point can be represented in direction and magnitude by the sides of a polygon, then the forces are in equilibrium C. if any number of forces acting at a point can be represented by the sides of a polygon taken in order, then the forces are in equilibrium D. if a polygon representing forces acting at a point is closed then forces are in equilibrium

A. if any number of forces acting at a point can be represented in direction and magnitude by the sides of a polygon taken in order, then the forces are in equilibrium

The algebraic sum of the resolved parts of a number of forces in a given direction is equal to the resolved part of their resultant in the same direction. This is as per the principle of A. independence of forces B. balance of force C. resolution of forces D. dependence of forces

C. resolution of forces

According to principle of transmissibility of forces, the effect of a force upon a body is A. the same at every point in its line of action B. different at different points in its line of action C. maximum when it acts at the center of gravity of a body D. minimum when it acts at the C.G. of the body

A. the same at every point in its line of action

D' Alembert's principle is used for A. reducing the problem of kinetics to equivalent statics problem B. stability of floating bodies C. determining stresses in the truss D. designing safe structures

A. reducing the problem of kinetics to equivalent statics problem

According to Lami's theorem A. if three forces acting at a point are in equilibrium, each force is proportional to the sine of the angle between the other two B. if three forces acting upon a particle are represented in magnitude and direction by the sides of a triangle, taken in order, they will be in equilibrium C. three forces acting at a point can be represented by a triangle, each side being proportional to force D. three forces acting at a point will be in equilibrium

A. if three forces acting at a point are in equilibrium, each force is proportional to the sine of the angle between the other two

The center of gravity of a triangle lies at the point of A. intersection of bisector of angles B. intersection of its altitudes C. concurrence of the medians D. intersection of diagonals

C. concurrence of the medians

Angle of friction is the A. the ratio of minimum friction force to friction force acting when the body is in motion B. ratio of limiting friction and normal reaction C. angle between normal reaction and the resultant of normal reaction and the limiting friction D. the ratio of minimum friction force to the friction force acting when the body is just about to move

C. angle between normal reaction and the resultant of normal reaction and the limiting friction

Frictional force encountered after commencement of motion is called: A. Post friction B. Limiting friction C. Dynamic friction D. Kinematic friction

C. Dynamic friction

A car of mass m is moving on a level circular track of radius R. If μs represents the static friction between the road and tyres of the car, the maximum speed of the car in circular motion is given by: A. √(μsRg) B. √(μsmRg) C. √(mRg/μs) D. √(Rg/μs)

A. √(μsRg) For smooth driving maximum speed of car v then mv/R=usmg v=√usRg

A ball is dropped from a satellite revolving around the earth at a height of 120 km. The ball will: A. fall down to earth gradually B. go far away in space C. continue to move with the same speed along the original orbit of satellite D. continue to move with same speed along a straight line tangentially to the satellite at that time

C. continue to move with the same speed along the original orbit of satellite The orbital speed of satellite is independent of mass of satellite, so the ball will behave as a satellite and will continue to move with the same speed in the original orbit.

The centre of mass of a system of particles does not depend upon: A. position of the particles B. forces acting on the particles C. relative distances between the particles D. masses of the particles

B. forces acting on the particles Centre of mass of system depends upon position and masses of particle Also, it depends upon relative distance between particles.

Which of the following is not a vector quantity? A. Work B. Displacement C. Electric field D. Acceleration

A. Work

particle of mass M is moving in a horizontal circle of radius R with uniform speed V. When it moves from one point to a diametrically opposite point, its: A. kinetic energy changes by MV^2/4 B. kinetic energy changes by MV^2 C. momentum does not change D. momentum changes by 2 MV

A. kinetic energy changes by MV^2/4 On the diametrically opposite points, the velocities have same magnitude but opposite directions. Therefore, change in momentum is MV-(-MV) = 2MV

When milk is churned, cream gets separated due to: A. Frictional force B. Centrifugal force C. Gravitational force D. Centripetal force

B. Centrifugal force

Two racing cars of masses m1 and m2 are moving in circles of radii r1 and r2 respectively. Their speeds are such that each makes a complete circle in the same time t. The ratio of the angular speeds of the first to the second car is: A. m1m2:r1r2 B. m1:m2 C. 1:1 D. r1:r2

C. 1:1 As time taken by both car to complete one revolution is same. As w=2n/T→ wo1/T, as T is same in both cases. Hence 'w' will also be same.