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1. 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.
Ans. No, it is not possible for the object to be travelling with a non-zero velocity if an object
experiences a net zero external unbalanced force.According to Newton's first law of motion,
a body continues to be in its state of rest or motion, unless it is acted upon by some
unbalanced external force
2. When a carpet is beaten with a stick, dust comes out of it. Explain.
Ans. When a carpet is beaten with a stick, dust comes out of it because carpet fibers vibrate
in forward and backward direction as the carpet is beaten but the loosely bound dust
particles due to inertia remain at rest and so they come out.
3. Why is it advised to tie any luggage kept on the roof of a bus with a rope?
Ans. It is advised to tie any luggage kept on the roof of a bus with a rope because when bus
moves the luggage also gets moving with the velocity same as that of the bus and in the same
direction but when bus changes direction or deaccelerates, due to inertia of motion luggage
moves in the same direction and because it is loosely attached to the bus and may get thrown
away from roof of buses.
4. A batsman hits a cricket ball which then rolls on a level ground. After covering a
short distance, the ball comes to rest. The ball slows to a stop because
(a) the batsman did not hit the ball hard enough.
(b) velocity is proportional to the force exerted on the ball.
(c) there is a force on the ball opposing the motion.
(d) there is no unbalanced force on the ball, so the ball would want to come to rest.
Ans. (c) there is a force on the ball opposing the motion.
5. 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 tons (Hint: 1 metric ton = 1000 kg.)
Ans. According to the question,
initial velocity of truck (u) = 0
distance = s= 400 m and time = 20 s
mass of truck = 7metric tons = 7000kg
400 =0 + 200a
400 = 200a
a = 400/200
therefore, = 14000 N
6. A stone of 1 kg is thrown with a velocity of 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?
Ans. since v
2
= u
2
+ 2as
0 = 20
2
+ 2 x a x 50 (object comes to rest so v=0)
-100a = 400
a = 400/-100 = - 4m / sec
2
therefore, the force of friction between the stone and the ice
= -4 N
7. An 8000 kg engine pulls a train of 5 wagons, each of 2000 kg, along a horizontal track.
If the engine exerts a force of 40000 N and the track offers a friction force of 5000 N,
then calculate:
(a) the net accelerating force
(b) the acceleration of the train; and
(c) the force of wagon 1 on wagon 2.
Ans. (a) The net accelerating force = Force exerted by engine - frictional force of track =
40000 - 5000 = 35000 N
(b) the acceleration of the train = a = F/m = = 35000/10000 =
(c) the force of wagon 1 on wagon 2
Wagon 1 will have to exert force on all 4 wagons next to it
so mass of other 4 wagons = = 8000 kg
F = ma = = 28000 N
8. An automobile vehicle has a mass of 1500 kg. What must be the force between the
vehicle and road if the vehicle is to be stopped with a negative acceleration of
?
Ans. since = -2550 N (negative sign symbolises acceleration in
opposite direction)
9. What is the momentum of an object of mass m, moving with a velocity v?
(a)
(b)
(c)
(d) mv
Ans. (d) mv
10. 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?
Ans. 200 N
11. Two objects, each of mass 1.5 kg, are moving in the same straight line but in opposite directions. The velocity of each object is before the collision during
which they stick together. What will be the velocity of the combined object after the
collision?
Ans. Momentum before collision took place =
= 0
Since the objects stick together after collision hence
momentum after the collision
= 3v
momentum before collision = momentum after collision
0 = 3v, v= 0/3 = 0
the velocity of the combined object after the collision (v)= 0
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.
Ans. No, it is not possible for the object to be travelling with a non-zero velocity if an object
experiences a net zero external unbalanced force.According to Newton's first law of motion,
a body continues to be in its state of rest or motion, unless it is acted upon by some
unbalanced external force
2. When a carpet is beaten with a stick, dust comes out of it. Explain.
Ans. When a carpet is beaten with a stick, dust comes out of it because carpet fibers vibrate
in forward and backward direction as the carpet is beaten but the loosely bound dust
particles due to inertia remain at rest and so they come out.
3. Why is it advised to tie any luggage kept on the roof of a bus with a rope?
Ans. It is advised to tie any luggage kept on the roof of a bus with a rope because when bus
moves the luggage also gets moving with the velocity same as that of the bus and in the same
direction but when bus changes direction or deaccelerates, due to inertia of motion luggage
moves in the same direction and because it is loosely attached to the bus and may get thrown
away from roof of buses.
4. A batsman hits a cricket ball which then rolls on a level ground. After covering a
short distance, the ball comes to rest. The ball slows to a stop because
(a) the batsman did not hit the ball hard enough.
(b) velocity is proportional to the force exerted on the ball.
(c) there is a force on the ball opposing the motion.
(d) there is no unbalanced force on the ball, so the ball would want to come to rest.
Ans. (c) there is a force on the ball opposing the motion.
5. 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 tons (Hint: 1 metric ton = 1000 kg.)
Ans. According to the question,
initial velocity of truck (u) = 0
distance = s= 400 m and time = 20 s
mass of truck = 7metric tons = 7000kg
400 =0 + 200a
400 = 200a
a = 400/200
therefore, = 14000 N
6. A stone of 1 kg is thrown with a velocity of 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?
Ans. since v
2
= u
2
+ 2as
0 = 20
2
+ 2 x a x 50 (object comes to rest so v=0)
-100a = 400
a = 400/-100 = - 4m / sec
2
therefore, the force of friction between the stone and the ice
= -4 N
7. An 8000 kg engine pulls a train of 5 wagons, each of 2000 kg, along a horizontal track.
If the engine exerts a force of 40000 N and the track offers a friction force of 5000 N,
then calculate:
(a) the net accelerating force
(b) the acceleration of the train; and
(c) the force of wagon 1 on wagon 2.
Ans. (a) The net accelerating force = Force exerted by engine - frictional force of track =
40000 - 5000 = 35000 N
(b) the acceleration of the train = a = F/m = = 35000/10000 =
(c) the force of wagon 1 on wagon 2
Wagon 1 will have to exert force on all 4 wagons next to it
so mass of other 4 wagons = = 8000 kg
F = ma = = 28000 N
8. An automobile vehicle has a mass of 1500 kg. What must be the force between the
vehicle and road if the vehicle is to be stopped with a negative acceleration of
?
Ans. since = -2550 N (negative sign symbolises acceleration in
opposite direction)
9. What is the momentum of an object of mass m, moving with a velocity v?
(a)
(b)
(c)
(d) mv
Ans. (d) mv
10. 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?
Ans. 200 N
11. Two objects, each of mass 1.5 kg, are moving in the same straight line but in opposite directions. The velocity of each object is before the collision during
which they stick together. What will be the velocity of the combined object after the
collision?
Ans. Momentum before collision took place =
= 0
Since the objects stick together after collision hence
momentum after the collision
= 3v
momentum before collision = momentum after collision
0 = 3v, v= 0/3 = 0
the velocity of the combined object after the collision (v)= 0
mkc708:
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Answered by
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A stone of 1 kg is thrown with a velocity of 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?
Answer:
V=2
2= u
2as
0 = 20
2 x a x 50 ( v=0)
-100a = 400
a = 400/-100 = - 4m
a =100 = -4m
= -4 m
100/4
= 25m
Answer:
V=2
2= u
2as
0 = 20
2 x a x 50 ( v=0)
-100a = 400
a = 400/-100 = - 4m
a =100 = -4m
= -4 m
100/4
= 25m
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