Q. No.A man pushes a wall and fails to displace it. He does:
1. negative work
2. positive but not maximum work
3. no work at all
4. maximum work
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A body constrained to move along the \({z}\)-axis of a coordinate system is subjected to constant force given by \(\vec{F}=-\hat{i}+2 \hat{j}+3 \hat{k}\) where \(\hat{i},\hat{j} \) and \(\hat{k}\) are unit vectors along the \({x}\)-axis, \({y}\)-axis and \({z}\)-axis of the system respectively. The work done by this force in moving the body a distance of \(4~\text m\) along the \({z}\)-axis will be:
1. \(15~\text J\)
2. \(14~\text J\)
3. \(13~\text J\)
4. \(12~\text J\)
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A block of mass \(m\) is being lowered by means of a string attached to it. The system moves down with a constant velocity. Then:
| 1. | the work done by gravity on the block is positive. |
| 2. | the work done by force, \(F \) (the force of the string) on the block is negative. |
| 3. | the work done by gravity is equal in magnitude to that done by the string. |
| 4. | All of the above are true. |
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A particle of mass m1 is moving with a velocity v1 and another particle of mass m2 is moving with a velocity v2. Both of them have the same momentum, but their kinetic energies are E1 and E2 respectively. If m1 > m2 then:
1.
2.
3.
4.
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A rigid body of mass \(m\) is moving in a circle of radius \(r\) with constant speed \(v.\) The force on the body is \(\dfrac{mv^2}{r}\) and is always directed towards the centre. The work done by this force in moving the body over half the circumference of the circle will be:
1. \(\dfrac{mv^{2}}{rπ}\)
2. \(mr^{2} \pi\)
3. zero
4. \(2 mv^{2} \pi\)
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The kinetic energy of a body is increased by 21%. The percentage increase in the magnitude of linear momentum of the body will be:
1. 10%
2. 20%
3. Zero
4. 11.5%
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A person of mass \(m\) ascends the stairs and goes up slowly through a height \(h\). Then,
| 1. | Work done by gravity is \(mgh\) |
| 2. | Work done by normal reaction is \(mgh\) |
| 3. | Work done by normal reaction is zero |
| 4. | Work done by gravity is stored as gravitational \(P.E\). |
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Mark the correct statement(s):
1. Internal forces cannot increase the kinetic energy of a system.
2. Internal forces may increase the kinetic energy of a system.
3. Work done by kinetic friction is always negative.
4. Both (2) & (3)
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Work done by frictional force during the walking of a man is:
1. positive
2. negative
3. zero
4. maybe positive or negative
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