Question 1 :
Avinash can run with a speed of $8 ms^{-1}$ against the frictional force of 10 N, and Kapil can move with a speed of $3 ms^{–1}$ against the frictional force of 25 N. Who is more powerful and why?
Question 3 :
Compare the power at which a butterfly of mass 1.0 g that flies upward at a rate of $0.5 ms^{–1}$ is moving upwards against the force of gravity. $(given g = 10 ms^{–2})$
Question 4 :
An object of mass 12 kg is at a certain height above the ground. If the potential energy of the object is 480 J, find the height at which the object is with respect to the ground. Given, g = 10 m $s^{-2}$.
Question 6 :
A green plant is carrying out photosynthesis. Is it a work?
Question 7 :
An object of mass m is moving with a constant velocity v. How much work should be done on the object in order to bring the object to rest?
Question 8 :
Work done on an object is defined as the magnitude of the force multiplied by the distance moved by the object in the direction of the applied force. The unit of work is joule:$ 1 joule = 1 newton \times 1 metre.$ Is the statement true or false?
Question 9 :
A person holds a bundle of hay over his head for 30 minutes and gets tired. Has he done some work or not?
Question 10 :
The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy?
Question 11 :
A battery lights a bulb. Describe the energy changes involved in the process.
Question 12 :
What are the various energy transformations that occur when you are riding a bicycle?
Question 13 :
An object of mass 15 kg is moving with a uniform velocity of 4 $ms^{-1}$. What is the kinetic energy possessed by the object?
Question 14 :
A certain household has consumed 250 units of energy during a month. How much energy is this in joules?
Question 15 :
The kinetic energy of an object of mass m moving with a velocity of 5 $\frac{m}{s}$ is 25 J. What will be its kinetic energy when its velocity is increased three times?
Question 16 :
A mass of 10 kg 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?
Question 17 :
Work done on an object by a force would be zero if the displacement of the object is zero.
Question 18 :
Let a constant force, F act on an object. Let the object be displaced through a distance, s in the direction of the force. Let W be the work done. So W = ?
Question 19 :
Soni says that the acceleration in an object could be zero even when several forces are acting on it. State true or false.
Question 20 :
The energy used in one hour at the rate of 1kW is called 1 kW h.
Question 21 :
An automobile engine propels a 1000 kg car (A) along a levelled road at a speed of $36 kmh^{–1}$.Now, suppose after travelling a distance of 200 m, this car collides with another stationary car (B) of same mass and comes to rest. Let its engine also stop at the same time. Now car (B) starts moving on the same level road without getting its engine started. Find the speed of the car (B) just after the collision.
Question 22 :
The kinetic energy of an object of mass m moving with a velocity of 5 $\frac{m}{s}$ is 25 J. What will be its kinetic energy when its velocity is doubled?
Question 23 :
The weight of a person on a planet A is about half that on the earth. He can jump upto 0.4 m height on the surface of the earth. How high he can jump on the planet A?
Question 24 :
Write an expression for the work done when a force is acting on an object in the direction of its displacement.
Question 25 :
Power is defined as the rate of doing work. The SI unit of power is watt. 1 W = 1 J/s.
Question 26 :
If an agent does a work W in time t, then power is given by: _________.
Question 28 :
Can there be displacement of an object in the absence of any force acting on it?
Question 29 :
The energy used in one hour at the rate of 1kW is called 1 kW h. TRUE OR FALSE?
Question 30 :
A rocket is moving up with a velocity $\upsilon$. If the velocity of this rocket is suddenly tripled, what will be the ratio of two kinetic energies?
Question 31 :
What are the two conditions that are really essential for a work to be done?
Question 32 :
Find the energy in kW h consumed in 10 hours by four devices of power 500 W each.
Question 33 :
Energy exists in nature in several forms such as kinetic energy, potential energy, heat energy, chemical energy etc. The sum of the kinetic and potential energies of an object is called its mechanical energy.
Question 34 :
An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. The initial and final points of the object lie on the same horizonta line. What is the work done by the force of gravity on th object
Question 35 :
If the object is starting from its stationary position, that is, u = 0, then work done, W = ?
Question 36 :
State true or false : There can be displacement of an object in the absence of any force acting on it.
Question 38 :
According to the law of conservation of energy, energy can only be transformed from one form to another; it can neither be created nor destroyed. The total energy before and after the transformation always remains constant.
Question 40 :
An electric heater is rated 1500 W. How much energy does it use in 10 hours?
Question 41 :
The relation connecting the initial velocity $\left(u\right)$ and final velocity $\left(v\right)$ of an object moving with a uniform acceleration a, and the displacement, s is__________.
Question 42 :
Certain force acting on a 20 kg mass changes its velocity from 5 $\frac{m}{s}$to 2 $\frac{m}{s}$. Calculate the work done by the force.
Question 43 :
Can any object have momentum even if its mechanical energy is zero?
Question 44 : <img style='object-fit:contain' src='https://teachmint.storage.googleapis.com/question_assets/cbse_ncert/61b1d2f2f59b460d7261f662.PNG' />
The above image shows, A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force shown in figure. Let us take it that the force acts on the object through the displacement. What is the work done in this case?
Question 45 :
An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. The initial and the final points of the path of the object lie on the same horizontal line. What is the work done by the force of gravity on the object?
Question 47 :
An electric bulb of 60 W is used for 6 h per day. Calculate the ‘units’ of energy consumed in one day by the bulb.
Question 48 :
A girl having mass of 35 kg sits on a trolley of mass 5 kg. The trolley is given an initial velocity of $4 ms^{–1}$ by applying a force. The trolley comes to rest after traversing a distance of 16 m. How much work is done by the girl?
Question 49 :
What is the formula of potential energy of an object ?
