Question:
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.
Answer:
We need to apply first law of motion and identify what force is applied which changes the velocity (state i.e. rest, direction, motion) of the ball. A force when applied can produce acceleration in body.
| Event |
Agent |
force and Action |
| A football player kicks a football |
football player |
push force, ball moves from rest. |
to another player of his team who
kicks the football towards the
goal. |
another player |
force, changes direction of ball. |
The goalkeeper of the opposite team
collects the football |
goal keeper |
force to stop ball
(ball velocity is zero now) |
and kicks it towards a player of
his own team |
goalkeeper |
force moves ball from rest to
motion in opposite direction. |
Force and Laws of Motion
Q 1.
A bullet of mass 10 g travelling horizontally with a velocity of 150 m/s strikes a stationary wooden block and comes to rest in 0.03 s. Calculate the distance of penetration of the bullet into the block. Also calculate the magnitude of the force exerted by the wooden block on the bullet.
Q 2.
Fill in the blanks :
It is dangerous to jump out of a moving bus because due to _________ one falls forward.
Q 3.
A stone of 1 kg is thrown with a velocity if 20
across the frozen surface of a lake and comes to rest after travelling a distance of 50 m.What is the force of friction between the stone and the ice ?
Q 4.
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 5.
A hockey ball of mass 200 g travelling at 10 m/s is struck by a hockey stick so as to return it along its original path with a velocity of 5 m/s.Calculate the change in momentum of the hockey ball by the force applied by the hockey stick.
Q 6.
Derive the unit of force using the second law of motion. A force of 5 N produces an acceleration of
on a mass
and an acceleration of 24
on a mass
.What acceleration would the same force provide if both the masses are tied together ?
Q 7.
Do action-reaction forces act on the same body ?
Q 8.
What would be the force required to produce an acceleration of 2
in a body of mass 12 kg ? What would be the acceleration if the force were doubled ?
Q 9.
A force of 5 N gives a mass
an acceleration of 10
,and a mass
,an acceleration of 20
.What acceleration would it give if both the masses were tied together ?
Q 10.
A bullet of mass 50 g is fired from a gun of mass 6 kg with a velocity of 400 m/s.Calculate the recoil velocity of the gun.
Q 11.
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 12.
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 13.
Can balanced forces move a body at rest ?
Q 15.
Define momentum of a body.
Q 16.
Derive the relation F = ma,where the symbols have their usual meanings.
Q 17.
State Newton's First Law of motion.
Q 18.
Fill in the blanks :
An umbrella protects us from rain it is based on the property of _____________.
Q 19.
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 20.
Which would require a greater force : accelerating a 2 kg mass at 5
or a 4 kg mass at 2
?
Q 21.
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 22.
What is the SI unit of force ?
Q 23.
What are balanced forces ?
Q 24.
Name the three types of inertia.
Q 25.
A person in a bus tends to fall backwards, when it starts suddenly ?
Q 26.
What is force ? What is inertia ? How is inertia measured ?
Q 27.
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 28.
If the set of forces acting on an object are balanced, then object
(a) must be at rest.
(b) must be moving
(c) must not be accelerating.
(d) none of these.
Q 29.
A truck starts from rest and rolls down a hill with a constant acceleration. It travels a distance of 400 m in 20 s. Find its acceleration. Find the force acting on it if its mass is 7 metric tonnes. (Hint: 1 metric tonne = 1000 kg.)
Q 30.
Using a horizontal force of 200 N, we intend to move a wooden cabinet across a floor at a constant velocity. What is the friction force that will be exerted on the cabinet?
Q 31.
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?
Q 32.
Fill in the blanks :
An athlete often jumps before taking a long jump. It is due to ________________.
Q 33.
Fill in the blanks :
________ is a measure of intertia.
Q 34.
Fill in the blanks :
The property of an object to resist changes in its rotational state of motion is called ________.
Q 35.
Define 1 Newton force.
Q 36.
Which principle is involved in the working of a jet plane?
Q 37.
A force of 4 N acts on a body of mass 2 kg for 4 s.Assuming the body to be initially at rest,find (a) its velocity when the force stops acting (b) the distance covered in 10 s after the force starts acting.
Q 38.
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 39.
A bullet of mass 10 g travelling horizontally with a velocity of 150
strikes a block and comes to rest in 0.03 s. Calculate the distance of penetration of the bullet into the block.Also, calculate the magnitude of the force exerted by the wooden block on the bullet.
Q 40.
Is momentum a scalar or vector ?
Q 41.
What is the total momentum of the bullet and the gun on firing ?
Q 42.
In the above question,which body undergoes greater change in momentum ?
Q 43.
Show that kg-
and N-s represent the same quantity.Which is that quantity ?
Q 44.
State Newton’s first law of motion. Hence define force and inertia.
Q 45.
State and deduce the principle of conservation of momentum.
Q 46.
Explain briefly any three applications of Newton’s third law of motion.
Q 48.
State Newtons second law of motion.
Q 49.
What are non-contact forces? Give examples.
Q 50.
Define 1N (Newton).
