Physics - Work Energy and Power
Exam Duration: 45 Mins Total Questions : 30
Law of conservation of linear momentum is applicable even in those cases where
- (a)
Newton's first law of motion does not hold good
- (b)
Newton's second law of motion does not hold good
- (c)
Newton's third law of motion does not hold good
- (d)
None of these
A body is moved along a stralight line by a machine delivering constant power. The distance between moved by in time t is proportioned to
- (a)
time t
- (b)
\(\sqrt t\)
- (c)
\((t)^{3/2}\)
- (d)
\(t^{2}\)
A bullet is fired from a rifle. If the rifle recoils freely, the kinectic energy of the rifle as compared to that of bullet is
- (a)
greater
- (b)
equal
- (c)
lesser
- (d)
nothing can be said.
A \(U^{238}\) nucleus emits an \(\alpha \)-particle is converted into thorium. If the velocity of \(\alpha \)-particle is 1.4 \(\times\)\(10^{5} ms^{-1}\); the velocity of thorium nucleus is
- (a)
\(2.4 \times 10^{5}?? ms^{-1}\)
- (b)
\(2.4 \times 10^{7}ms^{-1}\)
- (c)
\(3 \times 10^{8}ms^{-1}\)
- (d)
zero
A body of mass m1 travelling with velocity \(\upsilon\) suffers head on collision with a mass m2 at rest. Calculate the ratio of the kinetic energy., energy transfer is complete when
- (a)
m1 >m2
- (b)
m1 <m2
- (c)
m1 =m2
- (d)
m1 =2m2
A mass m moves with a velocity v and collides inelastically with another identical mass. After collision, the 1st mass moves with velocity \(v/\sqrt { 3 } \) in a direction perpendicular to the initial direction of motion. Find the speed of the second mass after collision.
- (a)
v
- (b)
\(\sqrt { 3v } \)
- (c)
\(\frac { 2 }{ \sqrt { 3 } } v\)
- (d)
\(\frac { v }{ \sqrt { 3 } } \)
If we lift a body from rest to a height h and the body is in static equilibrium, then net work done is:
- (a)
+ve
- (b)
-ve
- (c)
zero
- (d)
unity
If a body is moving on a horizontal rough road and the body is in dynamic equilibrium then net work done is:
- (a)
+ve
- (b)
-ve
- (c)
zero
- (d)
unity
A spring is held compressed so that its stored energy is 2.4 1. Its ends are in contact with masses I g and 48 g placed on a frictionless table. When the spring is released, the heavier mass will acquire a speed of:
- (a)
\(\frac { 2.4 }{ 49 } { ms }^{ -1 }\)
- (b)
\(\frac { 2.4\times 48 }{ 49 } { ms }^{ -1\ }\)
- (c)
\(\frac { { 10 }^{ 3 } }{ 7 } cms^{ -1 }\)
- (d)
\(\frac { { 10 }^{ 6 } }{ 7 } cms^{ -1 }\)
A 2 kg block drops vertically from a height of 40 cm on a spring whose force constant k is 1960 newton per metre. Then the maximum compression of the spring is:
- (a)
40 cm
- (b)
25 cm
- (c)
10 cm
- (d)
5 cm
A spring is compressed between two toy carts of masses m1 and m2. When the toy carts are released the spring exerts on each toy cart equal and opposite forces for the same time t. If the coefficients of friction \(\mu\) between the ground and the toy carts are equal, then the displacements of the toy carts are in the ratio:
- (a)
\(\frac { { s }_{ 1 } }{ { s }_{ 2 } } =\frac { { m }_{ 2 } }{ { m }_{ 1 } } \)
- (b)
\(\frac { { s }_{ 1 } }{ { s }_{ 2 } } =-\frac { { m }_{ 1 } }{ { m }_{ 2 } } \)
- (c)
\(\frac { { s }_{ 1 } }{ { s }_{ 2 } } =-{ \left( \frac { { m }_{ 2 } }{ { m }_{ 1 } } \right) }^{ 2 }\)
- (d)
\(\frac { { s }_{ 1 } }{ { s }_{ 2 } } =-{ \left( \frac { { m }_{ 1 } }{ { m }_{ 2 } } \right) }^{ 2 }\)
If we throw a body upwards with velocity of 4 m/s, at what height does its kinetic energy reduce to half of the initial value? (Take g = 10m s-2)
- (a)
4 m
- (b)
2 m
- (c)
1 m
- (d)
0.4 m
A body of mass 5 kg falls from a height of 20 m on the ground and it rebounds to a height of 0.2 m. If the loss in potential energy is used up by the body, then what will be the temperature rise? (Specific heat of the material = 0.09 cal gm-1 °C-1)
- (a)
5°C
- (b)
4°C
- (c)
8°C
- (d)
None of these
A machine which is 75 per cent efficient, uses 12 joule of energy in lifting up a 1 kg mass through a certain distance. The mass is then allowed to fall through that distance. The velocity at the end of its fall is: (in ms-1)
- (a)
\(\sqrt { 24 } \)
- (b)
\(\sqrt { 32 } \)
- (c)
\(\sqrt { 18 } \)
- (d)
\(\sqrt { 9 } \)
An object of mass m slides down a hill of height h of arbitrary shape and after travelling a certain horizontal path stops because of friction. The friction coefficient is different for different segments for the entire path but is independent of the velocity and direction of motion. The work that a force must perform to return the object to its initial position along the same path is:
- (a)
mgh
- (b)
2 mgh
- (c)
4mgh
- (d)
-mgh
If a ball is thrown upwards from the surface of the earth:
- (a)
the earth remains stationary while the ball moves upwards
- (b)
the ball remains stationary while the earth moves downwards
- (c)
the ball and the earth move towards each other
- (d)
the ball and the earth both move away from each other
A shell explodes and many pieces fly off in different directions. Which of the following is conserved?
- (a)
Kinetic energy
- (b)
Momentum
- (c)
Neither momentum nor KE
- (d)
Momentum and KE
In perfectly inelastic collisions, the relative velocity of the bodies:
- (a)
before impact is zero
- (b)
before impact is equal to that after impact
- (c)
after impact is zero
- (d)
is characterised by none of the above
A neutron moving with velocity u collides elastically with an atom of mass number A. If the collision is head on and the initial kinetic energy of neutron is E, then the final kinetic energy of the neutron after collision is:
- (a)
\({ \left( \frac { A+1 }{ A-1 } \right) }^{ 2 }E\)
- (b)
\({ \left( \frac { A-1 }{ A+1 } \right) }^{ 2 }E\)
- (c)
\(\left( \frac { A-1 }{ A+1 } \right) E\)
- (d)
\(\left( \frac { A+1 }{ A-1 } \right) E\)
A billiard ball moving with a speed of 5 m/s collides with an identical ball, originally at rest. If the first ball stops dead after collision, then the second ball will move forward with a speed of:
- (a)
10 ms-1
- (b)
5 ms-1
- (c)
2.5 ms-1
- (d)
1.0 ms-1
A ball of mass 0.2 kg is thrown vertically upwards by applying a force by hand. If the hand moves 0.2 m while applying the force and the ball goes upto 2 m height further. Find the magnitude of force. (Consider g = 10 m/s2)
- (a)
22 N
- (b)
4 N
- (c)
16 N
- (d)
20 N
A shell of mass 10 kg is moving with a velocity of 10 ms-1 when it blasts and forms two parts of mass 9 kg and 1 kg respectively. If the 1st mass is stationary, the velocity of the 2nd is:
- (a)
1 m/s
- (b)
10 m/s
- (c)
100 m/s
- (d)
1000 m/s
Water falls from a height of 60 m at the ratio of 15 kg/s to operate a turbine. The losses due to frictional forces are 10% of energy. How much power is generated by the turbine? (g = 10m/s2)
- (a)
12.3 kW
- (b)
7.0 kW
- (c)
8.1 kW
- (d)
10.2 kW
A motor is used to deliver water at a certain rate through a given horizontal pipe. To deliver n - times the water through the same pipe in the same time the power of the motor must be increased as follows:
- (a)
n - times
- (b)
n2 - times
- (c)
n3 - times
- (d)
n4 - times
The potential energy (in Joule) of a body of mass 2 kg moving in the XY-plane is given by U = 6x + 8y, where x and yare in metres. If the body is at rest at point (6 m,
4 m) at time t = 0, it will cross y-axis at time t equal to:
- (a)
\(\sqrt { 2 } \)s
- (b)
2 s
- (c)
3 s
- (d)
4 s
A ball is dropped from a height h. If the coefficient of restitution be e, then the body rebounds to a height of:
- (a)
eh
- (b)
e2h
- (c)
e3h
- (d)
e4h
A stationary bomb explodes into three pieces. One piece of 2 kg mass moves with a velocity of 8 ms-1 at right angles to the other piece of mass 1 kg moving with a velocity of 12 ms-1. If the mass of the third piece is 0.5 kg, then its velocity is:
- (a)
10 ms-1
- (b)
20 ms-1
- (c)
30 ms-1
- (d)
40 ms-1
- (e)
50 ms-1