Theoretical Verification of Law of Conservation

Q.

A mass of $10kg$ is at a point A on a table. It is moved to a point B. If the line joining A and B is horizontal, what is the work done on the object by the gravitational force? Explain your solution

Q.

The potential energy of a freely falling object decreases continuously. What happens to the loss of potential energy?

1. It is continuously converted into sound energy

2. It is continuously converted into kinetic energy

3. It is continuously destroyed

4. None of these

Q.

Water falls from a tap, down the streamline

1. Area decreases

2. Area increases

3. Velocity remains same

4. Area remains same

Q. Question 13
A ball is thrown vertically upwards with a velocity of 49 m/s. Calculate

(i) the maximum height to which it rises.
(ii) the total time it takes to return to the surface of the earth.

Q.

The work done by the gravity during descent of the projectile is

1. Positive

2. negative

3. zero

4. depends upon the sign convention where we used

Q.

What is dark energy

Q. A stone dropped from a tower reaches the ground in 5s. The height of the tower is___ m.

Q. Question 18
A ball thrown up vertically returns to the thrower after 6 s. Find

(a) the velocity with which it was thrown up,
(b) the maximum height it reaches, and
(c) its position after 4 s

Q.

Question 18
Using second law of motion, derive the relation between force and acceleration. A bullet of 10 g strikes sand-bag at a speed of ${10}^{3}m{s}^{-1}$ and gets embedded after travelling 5 cm. Calculate

(i) the resistive force exerted by the sand on the bullet
(ii) the time taken by the bullet to come

Q.

A car is going downhill with increasing speed. What happens to kinetic energy and potential energy.

1. Both increases

2. both decrease

3. PE increases KE decreses

4. KE increases and PE decreases

Q.

When a shot-put champion releases a 5.0 kg shot, it is at 1.5 m above the ground and traveling at 10 m/s. It reaches a maximum height of 5 m above the ground. What are the total mechanical energy, kinetic energy and potential energy of the shot at its maximum height?

1. 325 J, 75 J, 250 J

2. 450 J, 125 J, 325 J

3. 300 J, 100 J, 200 J

4. 350 J, 125 J, 225 J

Q.

A body is thrown up with a kinetic energy of $100J$ Find the potential energy at the topmost point.

Q. Question 15
A stone is thrown vertically upward with an initial velocity of 40 m/s. Taking $g=10m/s^2$, find the maximum height reached by the stone. What is the net displacement and the total distance covered by the stone?

Q.

A person standing on the edge of a cliff of height 40 m above the ground throws the first ball straight up with an initial velocity of 20 $\frac{m}{s}$, and then throws the second ball straight down with the same initial velocity 20 $\frac{m}{s}$. What are their respective velocities just before they hit the ground? (Take a = 10 $m/s^2$)

1. 20√2 m/s, 20√3 m/s

2. 20√3 m/s, 20√2 m/s

3. 20√3 m/s, 20√3 m/s

4. 20√2 m/s, 20√2 m/s

Q. Question 14
A stone is released from the top of a tower of height 19.6 m. Calculate its final velocity.

Q.

A $5kg$ ball is thrown upwards at a speed of $10m{s}^{-1}$. Assume $g$= $10m{s}^{-2}$

1. Calculate the maximum height attained by it.
2. Find the potential energy when it reaches the highest point.

Q.

A body of mass $2kg$ is thrown vertically upwards with K.E. $245J$. The acceleration due to gravity is $9.8m{s}^{-2}$. The K.E. of the body will become half at a height of

1. $25m$

2. $12.5m$

3. $6.25m$

4. $5m$

Q. State and prove law of conservation of energy in case of freely falling body?

Q.

A block of mass 50 kg is pulled up a slope with constant speed by applying an external force of 20 kgf parallel to the slope. The block moves through a distance of 4 m along the slope.

i) What is the work done by the external applied force?

ii) What is the energy stored when it reaches the vertical height of 3m (g = 10m/s²)

1. 700J, 1590J

2. 800J, 1500J

3. 920J, 1530J

4. 805J, 1670J

Q. Question 2
In the following example, try to identify the number of times the velocity of the ball changes: "A football player kicks a football to another player of his team who kicks the football towards the goal. The goalkeeper of the opposite team collects the football and kicks it towards a player of his own team". Also identify the agent supplying the force in each case.

Q. A ball of mass 200g falls from a height of 5m. What is its Kinetic Energy when it just reaches the ground?

1. 9.8 J
2. 98 J
3. none of these
4. 980 J

Q. A body of mass $2kg$ is thrown up vertically with kinetic energy of $490J$. If $g=9.8m/s^2$ , the height at which the kinetic energy of the body becomes half of the original values, is :

1. $50m$
2. $25m$
3. $19.6m$
4. $12.5m$

Q.

A ball is thrown vertically upwards with a velocity of $xm{s}^{–1}$. If the maximum height reached by the ball is $20m$, then the value of $x$ =__________$m{s}^{–1}.$

1. $10$

2. $15$

3. $20$

4. $25$

Q. A ball is thrown upwards from point A. It reaches up to point B and returns. What can be concluded?

1. Potential energy at A = potential energy at B
2. Kinetic energy at A = kinetic energy at B
3. Potential energy at B = kinetic energy at A
4. Potential energy at B = kinetic energy at B

Q.

A tennis ball dropped from a height of $2m$ rebounds only $1.5m$ after hitting the ground. What fraction of its energy is lost in the impact?

1. $\frac{1}{4}$

2. $\frac{1}{2}$

3. $\frac{1}{3}$

4. $\frac{1}{8}$

Q. A ball dropped from a $20m$ height loses $40$% of its energy on hitting the ground. Upto what height does the ball rebound?

1. $28m$
2. $8m$
3. $12m$
4. $20m$

Q.

Define the term: mechanical energy.

Q. The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy?

1. Yes
2. No
3. Yes, at certain instants
4. None of the above

Q. A body of mass 1 kg of thrown upwards with a velocity 20 m/s. It momentarily comes to rest after attaining a height of 18m. How much energy is lost due to air friction ?
$(g=10m/s^2)$

1. 10 J
2. 20 J
3. 30 J
4. 40 J

Q. A body of mass 2 kg has a potential energy of 800 J when it is at a certain height. If it begins to fall, its velocity when its Kinetic energy and Potential energy are equal is

1. $4m{s}^{-1}$
2. $400m{s}^{-1}$
3. $20m{s}^{-1}$
4. $80m{s}^{-1}$