Question:
The following is the distance-time table of an object in motion:
| Time in seconds |
Distance in meters |
| 0 |
0 |
| 1 |
1 |
| 2 |
8 |
| 3 |
27 |
| 4 |
64 |
| 5 |
125 |
| 6 |
216 |
| 7 |
343 |
(a) What conclusion can you draw about the acceleration? Is it constant, increasing, decreasing, or zero?
(b) What do you infer about the forces acting on the object?
Answer:
(a) Since the distance travelled in in equal intervals of time is not equal rather it is increasing. It means the object is moving with a non-uniform velocity. It is accelerating.
By looking at the table we find distance (S) ∝ t3 ...(I)
Let us check if acceleration is constant. We know that for fixed 'a', equation S = ut + ½at2 is valid.
In this case, u = 0, (since at t = 0, S = 0), ⇒ S = ½at2 or (S) ∝ t2 ... (II)
But from the table, we get S ∝ t3, we conclude, that 'a' is increasing.
(b) Since the object is in accelerated condition, According to Newton's Second Law, F ∝ a.
We can say, unbalanced force is acting on the object.
Force and Laws of Motion
Q 1.
Are action-reaction forces simultaneous ?
Q 2.
What is the unit of force in c.g.s system?
Q 3.
On what factor does inertia of a body depend ?
Q 4.
Do action-reaction forces produce the same magnitude of acceleration ?
Q 5.
Can every force produce motion in every object?
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.
What is the SI unit of impulse.
Q 9.
Fill in the blanks :
The study of motion of a body under the action of a force is called ______.
Q 10.
The masses of two objects are 2 kg and 20 kg. Which has greater inertia ?
Q 11.
A body of mass 25 kg has momentum of 125 kg m/s. What is the velocity of the body?
Q 12.
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 13.
When a branch of a tree is shaken, some of the fruits may fall down.Why ?
Q 14.
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 15.
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 16.
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 17.
Using second law of motion, derive the relation between force and acceleration.
Q 18.
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 19.
Can balanced forces change the shape and size of an object?
Q 20.
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 21.
What is the net momentum of gun and bullet system before firing?
Q 22.
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 23.
In the above question, which body is damaged more ?
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.
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 26.
Why is the person hurt less when he falls on a spongy surface?
Q 27.
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 28.
Why does a gunman get a jerk on a firing a bullet ?
Q 29.
Name any two applications of the law of conservation of linear momentum.
Q 30.
What is formula of impulse?
Q 31.
Fill in the blanks :
________ is the tendency of an object to resist a change in motion.
Q 32.
Force can change the shape and size of an object. Give an example.
Q 33.
Name the physical quantity that corresponds to the rate of change of momentum.
Q 34.
A body of mass 1 kg is kept at rest.A constant force of 6-0 N starts acting on it.Find the time taken by the body to move through a distance of 12 m.
Q 35.
What is the other name for Newton's first law of motion ?
Q 36.
What is one newton force ?
Q 37.
What acceleration is produced by a force of 5 N acting on a body of mass 20 kg ?
Q 38.
Which is having higher value of momentum ? A bullet of mass 10 g moving with a velocity of 400 m/s or a cricket ball of mass 400 g thrown with the speed of 90 km/hr.
Q 39.
What are balanced and unbalanced forces?
Q 40.
Which law of motion gives the measure of force?
Q 41.
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 42.
Discuss briefly Galileo's ideas about motion.
Q 43.
State and deduce the principle of conservation of momentum.
Q 44.
What a force can do?
Q 45.
What are non-contact forces? Give examples.
Q 46.
An object of mass 5 kg is moving with a velocity 4 m/s. A constant force of 20 N acts on the object. What will be the velocity after 3 s.
Q 47.
Two persons manage to push a motorcar of mass 1200 kg at a uniform velocity along a level road. The same motorcar can be pushed by three persons to produce an acceleration of 0.2m s-2. With what force does each person push the motorcar?
(Assume that all persons push the motorcar with the same muscular effort.)
Q 48.
Fill in the blanks :
When we shake a branch of a mango tree the mangoes fell down, this happens because of ___________.
Q 49.
Fill in the blanks :
It is dangerous to jump out of a moving bus because due to _________ one falls forward.
Q 50.
What are balanced forces?
