Negative Work

Q.

What should be the angle between force and the displacement for maximum and minimum work?

Q.

In a tug of war one team gives way to the other what work is being done and by whom

Q.

A force of $10N$ displaces a body by $5m$, the angle between force and displacement is ${60}^o$, then find the work done.

Q.

A man carrying a bucket of water, walking on a level road with a uniform velocity does no work.

1. True
2. False

Q. Figure shows four situations in which a force acts on a box while the box slides rightward a distance d across a frictionless floor. The magnitude of the forces are identical with their orientations as shown. Identify under which condition the work done on the box during the displacement will be negative.

1. 
2. 
3. 
4. 

Q. A rigid body of mass $m\text{kg}$ is lifted with uniform velocity by a man to a height of $1\text{m}$ in $30\text{seconds}$. Another man lifts the same mass with uniform velocity to the same height in $60\text{seconds}$. The work done on the body against gravity by them are in the ratio

1. $1:2$
2. $1:1$
3. $2:1$
4. $4:1$

Q.

In tug of war, the team that exerts a larger tangential force on the ground wins. Consider the period in which a team is dragging the opposite team by applying a larger tangential force on the ground. List which of the following works are negative?

i.Work by the winning team on the losing team

ii.Work by the losing team on the winning team

iii.Work by the ground on the winning team

iv.Work by the ground on the losing team

1. ii, iii, iv

2. I, ii, iii, iv

3. None of these

4. ii, iv

Q. A ball is thrown vertically upwards, it reaches the height $h$ and then returns to the initial position. Work done by gravity when ball moves upwards is $W_1$ and $W_2$ when ball moves in downward direction. Then

1. $W_1=mgh,W_2=mgh$
2. $W_1=mgh,W_2=-mgh$
3. $W_1=-mgh,W_2=mgh$
4. $W_1=-mgh,W_2=-mgh$

Q.

If the angle between force F and displacement s is 60^o , then the work done is,

1. Fs

2. F/s

3. F X s/2

4. 2 Fs

Q. A particle of mass $m=3kg$ moves along a straight line $4y-3x=2$ where $x$ and $y$ are in metre, with constant velocity $v=5m{s}^{-1}$. The magnitude of angular momentum about the origin is

1. $12kg{m}^2{s}^{-1}$
2. $6.0kg{m}^2{s}^{-1}$
3. $4.5kg{m}^2{s}^{-1}$
4. $8.0kg{m}^2{s}^{-1}$

Q. A rigid body of mass $m\text{kg}$ is lifted with uniform velocity by a man to a height of $1\text{m}$ in $30\text{seconds}$. Another man lifts the same mass with uniform velocity to the same height in $60\text{seconds}$. The work done on the body against gravity by them are in the ratio

1. $1:2$
2. $1:1$
3. $2:1$
4. $4:1$

Q. A ball is thrown vertically upwards, it reaches the height $h$ and then returns to the initial position. Work done by gravity when ball moves upwards is $W_1$ and $W_2$ when ball moves in downward direction. Then

1. $W_1=mgh,W_2=mgh$
2. $W_1=mgh,W_2=-mgh$
3. $W_1=-mgh,W_2=mgh$
4. $W_1=-mgh,W_2=-mgh$

Q. The Undertaker brags about stopping a moving car with bare hands. To prove himself he stands infront of a moving car coming towards him and surprisingly stops the car in 10 seconds after initial contact.The work done by him in this duration will be

1. positive
2. negative
3. zero
4. can't be said.

Q. Assertion : A body is moved from $x=2$ to $x=1$, under a force $F=4x$, the work done by the force is negative.
Reason: Force and displacement are in opposite directions.

1. Both Assertion and Reason are true but Reason is not the correct explanation of Assertion
2. Assertion is true but the Reason is false
3. Both Assertion and Reason are true and the Reason is correct explanation of Assertion
4. Assertion is false but the Reason is true

Q. two point like charges having magnitude $+16\mu C$ and $-9\mu C$ are separated by a distance $10cm$ in air. The resultant electric field will be zero.

1. 20 cm
2. 30 cm
3. 10 cm
4. 4 cm

Q. The spring shown in the figure is unstretched when a man starts pulling on the cord. The mass of the block is $M$. If the man exerts a constant force $F$, find (a) the amplitude and the time period of the motion of the block, (b) the energy stored in the spring when the block passes through the equilibrium position and (c) the kinetic energy of the block at this position.

Q. A bolt is being tightened by a $20N$ force applied to a $25cm$ long wrench at an angle of ${60}^{\circ }$ with the wrench. The magnitude of the torque is

1. $100\sqrt{3}$
2. $500\sqrt{3}$
3. $250\sqrt{3}$
4. $250$

Q.

If force is applied at an angle $\theta$ to the direction of displacement of a body, how will you derive the amount of work done?

Q.

What should be the angle between the direction of force and direction of displacement if

1. Work done is zero and
2. Work done is negative?

Q. Figure shows four situations in which a force acts on a box while the box slides rightward a distance d across a frictionless floor. The magnitude of the forces are identical with their orientations as shown. Identify under which condition the work done on the box during the displacement will be negative.

1. 
2. 
3. 
4. 

Q.

A person pulls a body on a horizontal surface by applying a force of 5.0 N at an angle of 30^o, with the horizontal. Find the work done by this force in displacing the body through 2.0 m.

1. $5\sqrt{3}J$

2. $6\sqrt{2}J$

3. $7\sqrt{3}J$

4. $4\sqrt{3}J$

Q. A rod of mass $M$ and Length $L$ is hinged at its one end and carries a block of mass m at its lower end. A spring of force constant $k_1$ is installed at distance $a$ from the hinge and another of force constant $k_2$ at a distance $b$ as shown in the figure. If the whole arrangement rests on a smooth horizontal table top, the frequency of vibration is

1. $\frac{1}{2\pi }\sqrt{\frac{k_1{a}^2+k_2{b}^2}{L^2(m+\frac{M}{3})}}$
2. $\frac{1}{2\pi }\sqrt{\frac{k_2+k_1}{M+m}}$
3. $\frac{1}{2\pi }\sqrt{\frac{k_2+k_1\frac{a^2}{b^2}}{4\frac{M}{3}+m}}$
4. $\frac{1}{2\pi }\sqrt{\frac{k1+\frac{k_2{b}^2}{a^2}}{\frac{4}{3}m+M}}$

Q. Forces can do negative work.

1. False
2. True

Q. A spring of force constant $k$ is cut in two parts at its one-third length. When both the parts have same elongation, the work done in the two parts will be (Spring constant of a spring is inversely proportional to length of spring)

1. Equal to both
2. Greater for the longer part
3. Greater for the shorter part
4. Data insufficient

Q.
The applied force F is enough to move, both block A and B together.The frictional force between A nad B does ________ work on A and _________ work on B.

1. positive, positive
2. positive, negative
3. negative, negative
4. negative, positive

Q. A block is placed on a rough horizontal surface. The minimum force required to slide the block is

1. $F\cos \theta$
2. $\mu mg$
3. $\frac{\mu mg}{\sqrt{1+{\mu }^2}}$
4. $Allofthese$

Q. A rod of mass $M$ and length $L$ is hinged at its one end and carries a particle of mass $m$ at its lower end. A spring of force constant $k_1$ is installed at distance $a$ from the hinge and another of force constant, $k_2$ at a distance $b$ as shown in the figure. The whole arrangement rests on a smooth horizontal table top. Find the frequency of vibration.

Q. In case of non conservative force work done along all possible path scan not be same.

1. True
2. False

Q. A man of weight W is standing on a lift which is moving upward with an acceleration a. The apparent weight of the man is

1. $W(1+\frac{a}{g})$
2. W
3. $W(1-\frac{a}{g})$
4. $W(1-\frac{a^2}{g^2})$

Q. A man runs a distance 'S' on a level road. The same man up a hill with the same velocity through the same distance. When does he do more work?