Work Done as Dot Product

Q. A cord is used to lower vertically a block of mass M by a distance d with constant downward acceleration Work done by the cord on the block is

1. 
2. 
3. 
4. Mgd

Q. The work done in pulling up a block of wood weighing 2 kN for a length of 10m on a smooth plane inclined at an angle of ${15}^{\circ }$ with the horizontal is

1. 9.36 kJ
2. 19.82 kJ
3. 5.17 kJ
4. 18.91 kJ

Q. A man moves from a point on the horizontal surface of earth (assumed smooth) and reaches diagonally opposite point of a room. What is the work done by him –

1. Nothing can be said.
2. Negative
3. Positive
4. Zero

Q. Work is always said to be done by -

1. none
2. the body
3. displacement
4. a force

Q.

A small block of mass 2 kg is kept on a rough inclined surface of inclination $\theta ={30}^{\circ }$ fixed in a lift. The lift goes up with a uniform speed of 1 m$s^{-1}$ and the block does not slide relative to the inclined surface. The work done by the force of friction on the block in a time interval of 2 s is.

1. Zero

2. 9.8 J

3. 16.9 J

4. 29.4 J

Q. A ball is released from the top of a tower. The ratio of work done by force of gravity in first, second and third second of the motion of the ball is

1. 1 : 2 : 3
2. 1 : 4 : 9
3. 1 : 3 : 5
4. 1 : 5 : 3

Q.

A cord is used to lower vertically a block of mass M by a distance d with constant downward acceleration $\frac{g}{4}$ . Work done by the cord on the block is

1. 

2. Mgd

3. 

4. 

Q.

A force of 5 N acts on a 15 kg body initially at rest. The work done by the force during the first second of motion of the body is

1. 5 J

2. 

3. 

4. 6 J

Q.

A particle of mass 0.01 kg travels along a curve with velocity given by $4\hat{i}+16\hat{k}m{s}^{-1}$. After some time, its velocity becomes $8\hat{i}+20\hat{j}m{s}^{-1}$due to the action of a conservative force. The work done on particle during this interval of time is

1. 0.32 J

2. 6.9 J

3. 9.6 J

4. 0.96 J

Q.

The mass of a bucket containing water is 10 kg. What is the work done in pulling up the bucket from a well of depth 10 m if water is pouring out at a uniform rate from a hole in it and there is loss of 2kg of water from it while it reaches the top $(g=10m/se{c}^2)$

1. 1000 J

2. 800 J

3. 500 J

4. 900 J