Question:
An object experiences a net zero external unbalanced force.Is it possible for the object to be travelling with a non-zero velocity ? If yes,state the conditions that must be placed on the magnitude and direction of the velocity.If no,provide a reason.
Answer:
Yes,when external unbalanced force on an object is zero,the object can be travelling with a non-zero velocity.The necessary conditions are : (i) The object should already be moving with a uniform speed along a straight line, (ii) There should be no change in magnitude of velocity and also no changc in the direction of motion,(iii) The resistance to motion due to air must be zero,(iv) The resistance to motion due to friction between the object and the ground must be zero.
If any of the four conditions stated above is not met with,the answer will be ‘No’.This is because external unbalanced force is needed for initiating the motion and also for any subsequent change (decrease/increase) in its velocity.
Force and Laws of Motion
Q 1.
A car weighs 1500 kg.Its speed time graph is shown in Fig. Calculate the force required at the end of 5 seconds to bring the car to a stop within one second.
Q 2.
While driving on a highway, an insect strikes on the car windshield and splatters. Which experiences greater impact (force): an insect or the windshield?
Q 3.
What is the total momentum of a bullet and a gun before firing?
Q 4.
Can balanced forces change the shape and size of an object?
Q 5.
Fill in the blanks :
The study of motion of a body under the action of a force is called ______.
Q 6.
Can balanced forces change the shape and size of a body ?
Q 7.
On what factor does inertia of a body depend ?
Q 8.
Are action-reaction forces simultaneous ?
Q 9.
Using second law of motion, derive the relation between force and acceleration.
Q 10.
A TV set is lying on a table. The TV set experiences a gravitational force (pull) downwards (FW) by the Earth. It also experiences a force on it due to table in contact i.e. (FTable-TV) in upward direction. Do these forces form an action-reaction pair? Do these forces follow Newton's third Law of motion?
Q 11.
Can every force produce motion in every object?
Q 12.
When a branch of a tree is shaken, some of the fruits may fall down.Why ?
Q 13.
Do action-reaction forces produce the same magnitude of acceleration ?
Q 14.
Honey and Sunny are two friends.Both are financially well off.Honey is fond of driving an SUV while Sunny enjoys driving Tata Nano.Honey explains to Sunny the risks of driving a light vehicle and Sunny explains to Honey the cost factor.
Read the above passage and answer the following questions :
(i) With whom do you agree,with Honey or with Sunny?
(ii) Explain, why?
(iii) Which values of life do you learn from this discussion?
Q 15.
State Law of conservation of momentum.
Q 16.
In the above question, which body is damaged more ?
Q 17.
What is the unit of force in c.g.s system?
Q 18.
It is difficult to balance our body when we accidentally slip on a peel of banana. Explain why?
Q 19.
From a rifle of mass 4 kg, a bullet of mass 50 g is fired with an initial velocity of 35 m/s. Calculate the initial recoil velocity of the rifle.
Q 20.
A motorcar of mass 1200 kg is moving along a straight line with a uniform velocity of 90 km/h. Its velocity is slowed down to 18 km/h in 4 s by an unbalanced external force. Calculate the acceleration and change in momentum. Also calculate the magnitude of the force required.
Q 21.
Fill in the blanks :
The momentum of an object is the product of its _____ and _______ and has the same direction as that of the ________.
Q 22.
A man pushes a box of mass 50 kg with a force of 80 N.What will be the acceleration of the box ? What would be the acceleration if the mass were halved ?
Q 23.
For how long should a force of 100 N act on a body of mass 20 kg so that it acquires a velocity of 100 m/s ?
Q 25.
Why does a person in a bus tend to fall forward when it stops suddenly ?
Q 26.
A body of mass 25 kg has momentum of 125 kg m/s. What is the velocity of the body?
Q 27.
Fill in the blanks :
When a car enters a curved path, the person sitting in it is thrown outwards. This is because of the property of ______________.
Q 28.
Fill in the blanks :
When a bus starts suddenly, the bus passengers standing in the bus tend to fall backwards. It is due to _______________.
Q 29.
Give an example that force can make a stationary body move.
Q 30.
When a force acts on a body, what are the two essential effects it can produce?
Q 31.
A feather of mass 10 g is dropped from a height.It is found to fall down with a constant velocity.What is the net force acting on it ?
Q 32.
A hammer of mass 500 g,moving at 50 m/s,strikes a nail.The nail stops the hammer in a very short time of 0.01 s.What is the force of the nail on the hammer ?
Q 33.
What are unbalanced forces ?
Q 34.
Discuss briefly Galileo's ideas about motion.
Q 35.
Why does a gun recoil on firing ? Obtain an expression for recoil velocity of gun.
Q 36.
Give atleast four applications of Newton’s second law of motion.
Q 37.
Why is it advised to tie any luggage kept on the roof of a bus with a rope?
Q 38.
A hammer of mass 500 g, moving at 50 m/s, strikes a nail. The nail stops the hammer in a very short time of 0.01 s. What is the force of the nail on the hammer ?
Q 39.
Fill in the blanks :
An imaginary co-ordinate system which is either at rest or in uniform and where Newton's laws are valid is called an _______ frame of reference.
Q 40.
What is the momentum of a man of mass 75 kg when he walks with a velocity of 2 m/s ?
Q 41.
Two hockey players of opposite teams,while trying to.hit a hockey ball on the ground collide and immediately become entangled.One has a mass of 60 kg,and was moving with a velocity 5.0 m/s,while the other has a mass of 55 kg and was moving faster with a velocity of 6.0 m/s towards the first player,In which direction and with what velocity will they move after they become entangled ? Assume that the frictional force acting between the feet of the two players and ground is negligible.
Q 42.
What are balanced forces ?
Q 43.
Is momentum a scalar or vector ?
Q 44.
What is the total momentum of the bullet and the gun on firing ?
Q 45.
In the above question,which body undergoes greater change in momentum ?
Q 46.
Define momentum of a body.
Q 47.
What acceleration is produced by a force of 5 N acting on a body of mass 20 kg ?
Q 48.
An unloaded truck weighing 2000 kg has a maximum acceleration of 0.4
.What is the maximum acceleration, when it carries a load of 2000 kg ?
Q 49.
Name any two applications of the law of conservation of linear momentum.
Q 50.
Show that kg-
and N-s represent the same quantity.Which is that quantity ?
