Question:
Akhtar,Kiran and Rahul were riding in a motorcar that was moving with a high velocity on an expressway when an insect hit the windshield and got stuck on the windscreen. Akhtar and Kiran started pondering over the situation. Kiran suggested that the insect suffered a greater change momentum as compared to the change in momentum of the motorcar (because the chanee in the velocity of the insect was much more than that of the motorcar). Akhtar said that smce the motorcar was moving with a larger velocity, it exerted a larger force on the insect.And as a result,the insect died.Rahul whUe putting an entirely new explanation said that both the motorcar and the msect experienced the same force and a change in their momentum.Comment on these suggestions.
Answer:
Ans The suggestion made by Kiran that insect suffered a greater change in momentum as compared to the change in momentum of the motor car is wrong.The suggestion made by Akhtar that motor car exerted a larger force on the insect because of large velocity of motor car is also wrong. The explanation put forward by Rahul is correct.On collision of insect with motor car,both experience the same force as action and reaction are always equal and opposite.Further,changes in their momenta are also the same.Only the signs of changes in momenta are opposite, i.e.,change in momenta of the two occur in opposite directions,though magnitude of change in momentum of each is the same.
Force and Laws of Motion
Q 1.
Are action-reaction forces simultaneous ?
Q 2.
Do action-reaction forces produce the same magnitude of acceleration ?
Q 3.
On what factor does inertia of a body depend ?
Q 4.
Can every force produce motion in every object?
Q 5.
What is the unit of force in c.g.s system?
Q 6.
Explain why a player lowers his hands while catching a cricket ball.
Q 7.
It is difficult to balance our body when we accidentally slip on a peel of banana. Explain why?
Q 8.
The masses of two objects are 2 kg and 20 kg. Which has greater inertia ?
Q 9.
What is the SI unit of impulse.
Q 10.
Fill in the blanks :
The study of motion of a body under the action of a force is called ______.
Q 11.
An object of mass 1 kg travelling in a straight line with a velocity of 10 m/s collides with, and sticks to, a stationary wooden block of mass 5 kg. Then they both move off together in the
same straight line. Calculate the total momentum just before the impact and just after the impact. Also, calculate the velocity of the combined object.
Q 12.
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 13.
A body of mass 25 kg has momentum of 125 kg m/s. What is the velocity of the body?
Q 14.
A man pushes a box of mass 50 kg with a force of 80 N. What will be the acceleration of the box due to this force? What would be the acceleration if the mass were doubled ?
Q 15.
Can balanced forces change the shape and size of an object?
Q 16.
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.
Q 17.
When a branch of a tree is shaken, some of the fruits may fall down.Why ?
Q 18.
Derive the relation F = ma,where the symbols have their usual meanings.
Q 19.
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 20.
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 21.
What is the net momentum of gun and bullet system before firing?
Q 22.
State Newton’s second law of motion and establish that F = ma where symbols have their usual meanings.
Q 23.
Fill in the blanks :
A cyclist on a levelled road does not come to rest immediately even he stops pedalling. It is due to ______________.
Q 24.
A certain force exerted for 1 -2 s raises the speed of an object from 1.8 m/s to 4.2 m/s. Later,the same force is applied for 2 second. How much does the speed change in 2 s ?
Q 25.
When a force acts on a body, what are the two essential effects it can produce?
Q 26.
Is momentum a scalar or vector ?
Q 27.
A person in a bus tends to fall backwards, when it starts suddenly ?
Q 28.
State Newton’s first law of motion. Hence define force and inertia.
Q 29.
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 30.
Fill in the blanks :
When we shake a branch of a mango tree the mangoes fell down, this happens because of ___________.
Q 31.
Write the SI and CGS unit of force.
Q 32.
If the body is found to be accelerated, is the force acting on it balanced or unbalanced?
Q 33.
What is the total momentum of a bullet and a gun before firing?
Q 34.
Name the physical quantity that corresponds to the rate of change of momentum.
Q 35.
Which principle is involved in the working of a jet plane?
Q 36.
What is the momentum of a man of mass 75 kg when he walks with a velocity of 2 m/s ?
Q 37.
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 38.
Two objects of masses 100 g and 200 g are moving along the same line in the same direction with velocities of 2 m/s and 1 m/s,respectively.They collide and after the collision, the first object moves at a velocity of 1.67 m/s in the same direction.Determine the velocity of the second object
Q 39.
Can balanced forces move a body at rest ?
Q 40.
Name the unbalanced force that stops a ball rolling on the ground.
Q 41.
What is the other name for Newton's first law of motion ?
Q 42.
In the above question,which body undergoes greater change in momentum ?
Q 43.
In the above question, which body is damaged more ?
Q 45.
A ball is thrown vertically upwards. What is its momentum at the highest point ?
Q 46.
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 47.
Why does a gunman get a jerk on a firing a bullet ?
Q 48.
Name any two applications of the law of conservation of linear momentum.
Q 49.
Explain what is meant by momentum of a body.Is it a scalar or a vector ? What are its units ?
Q 50.
Why does a gun recoil on firing ? Obtain an expression for recoil velocity of gun.
