UNIT#01 FORCE AND MOTION Flashcards
A cyclist moves along a circular path of a radius of 70m if he completes one round in 11 sec.
Calculate the total length of the path:
440m
(Total Length of the hemisphere: 2πr)
A body is projected horizontally from the top of a cliff with a velocity of 9.8 m/s. What time elapses before horizontal and vertical velocities become equal?
1 sec
(➡Horizontal Component: vx=9.8 ms-1
➡Vertical Component: vy=gt
Two bullets are fired simultaneously, horizontally and at different speeds from the same place. Which bullet will hit the ground first?
Both will reach simultaneously
(T=√2h/g)
➡Mass does not have any role
A body is moving along a straight path. What will happen to the body in the absence of an external field;
It will move at the same speed along the same straight path
(Newton’s First Law)
A person is standing on a bus. When the bus starts moving forward suddenly:
The person moves backwards
(Due to inertia)
A ship of mass 3x10^7 kg initially at rest is pulled by a force of 5x10^4 N through a distance of 3m. Assuming that the resistance due to water is negligible., the speed of the ship is;
0.1 m/s
(v=√2aS)
(a=F/m)
Which of the following is an example of inelastic collision:
➡If there is loss of Kinetic Energy
The collision between two vehicles
Mud thrown on a wall and sticking to it is an example for:
Perfectly inelastic collision
(if two bodies stick together and move with common velocity, then perfectly inelastic collision)
A body moves 6m North, 8m East and 10m vertically upwards, what is its resultant displacement from the initial position;
10√2m
The instantaneous acceleration is the limit of average acceleration is Δt➡0 is given by
The formula of instantaneous acceleration
If an object is moving with a constant velocity of 20ms-1 towards the north then its acceleration will be;
0 ms-2
(as it is moving with constant velocity)
The retardation is defined as;
Decrease in velocity per unit time
Consider the acceleration, velocity and displacement of a tennis ball as it falls to the ground and bounces back. Directions of which these changes in the process:
➡Displacement
➡Velocity
A particle foes from from x= -2m, y=3m, z=1m to x=3m, y=-1m, z=4m. Its displacement is;
(5m)i - (4m)j + (3m)k
(Displacement= B-A)
The length of the path of a particle is equal to the magnitude of the displacement of that particle. The shape of the path possible
Straight Line
The shortest distance between two points is called
Displacement
Two cars moving in opposite directions with speed v. What is the magnitude of their relative velocity?
2v
(For bodies moving in opposite directions relative velocities add up)
A body can have constant velocity it follows;
Rectilinear motion
A man in a car is moving with a velocity of 36 km/hr. His speed with respect to the car is;
Zero
(man is at rest)
A man leaves his house for a cycle ride. He comes back to his house half an hour after covering a distance of one km. What is his average velocity for the ride;
5ms-1
If the slope of a velocity-time graph gradually decreased, the body is said to be moving with
Positive acceleration
If the force acting on a body is doubled, then acceleration becomes:
Doubled
When the force of 1N is applied on a body of mass of 100g then the acceleration would be;
10 ms-2
A mass of 10kg moves with an acceleration of 10ms-2, then force on it is;
100N
Which law of motion defines force?
1st Law
A force of 12N gives an object an acceleration of 4 m/s2. The force required to give it an acceleration of 10ms-2 is:
30N
When a force of 4N acts on a mass of 2kg for a time of 2 sex, what is the rate of change in momentum
4 kgms-2
Which is a statement of the principle of conservation of momentum?
The total momentum of a system of interacting bodies remains constant, providing no external force acts
The average force necessary to stop a hammer with 25 Ns momentum in 0.05 sec expressed in ‘N’ is:
500
In which of the following cases forces may not require to keep them;
The momentum of a particle remains constant
A force of 6 N acts on a mass of 1kg which acquires a velocity of 30 ms-1. The time for which the force acts as;
5 sec
A force of 100 Dynes acts on a mass of 5 g for 10 sec. The velocity produced is:
200 cm/sec
A gun after firing recoils due to;
Conservation of momentum
A player takes 0.1 sec in catching a ball of mass 150 g moving with a velocity of 20 m/s. The force imparted by the ball on the hands of the player is;
30 N
a ball of mass 2kg travelling at 8ms-1 strikes a ball of mass 4kg travelling at 2ms-1. Both balls are moving along the same straight line.
After the collision, both balls move at the same velocity v. What is the magnitude of the velocity v?
4 ms-1
Two similar spheres, each of mass m and travelling with speed v, are moving towards each other
The spheres have a head-on elastic collision. Which statement is correct
The total kinetic energy after impact is mv2
Two railway trucks of masses m and 3m move towards each other in opposite directions with speeds 2v and v respectively. These trucks collide and stick together.
What is the speed of the trucks after the collision?
v/4
The collision between the two bodies is elastic if the bodies are:
➡Solid
➡Hard
When a very heavy ball ‘B1’ collides with a stationary target ‘B2’ of negligible mass, after the collision the final velocity of ball ‘B2’ will;
Become doubled as compared to B1
A shell explodes into four equal parts. Which one of the following is conserved?
Momentum
A handball is tossed vertically upward with a velocity of 19.6 meters per second. Approximately how high will it rise?
20m
Which shows the correct relation between time of flight T and maximum height H?
H=gT2/8
At the maximum height on the trajectory which projectile becomes zero
Vertical Velocity
Time taken by a projectile to reach maximum height is t=
2vi sinΘ/g
Two projectiles are projected at an angle of 20° and 70° with the same velocity one has a longer range
Both have the same range
The path followed by a projectile is known as its:
Trajectory
A projectile is fired horizontally with an initial speed of 20 m/s. Its horizontal speed 3s
20 m/s
(Horizontal component of speed remains constant)
For which of the following angles range is maximum?
43°
A bullet is fired horizontally from a rifle at a distant target. Ignoring the effect of air resistance, what is the horizontal and vertical acceleration of the bullet?
Horizontal➡0
Vertical➡9.8 ms-2
Under what condition an object will have zero displacement but non-zero distance
Circular Motion
What is the acceleration of a projectile relative to another projectile:
0
If the flock of birds is flying, the total momentum will be zero if;
Very tired and coming down to rest
The slope of the distance-time graph will always be;
Positive
At what angle of projection of a projectile the range becomes half of its maximum value;
15°
If we drop an object, its initial velocity is zero. How far will fall in time ‘t’?
4.9 t2
The newton-second is a unit of;
➡Impulse
➡Momentum
The accelerating frame of reference which has constant acceleration is;
free falling body on earth
Vertical velocity vs time graph for a projectile motion
Varies linearly
Pseudo forces arise in;
The accelerating frame of reference
The magnitude of displacement is;
Straight line distance between the initial and final position
A car travels 30m towards the east, then it takes to turn and travels 40 m towards the west, its average velocity after 60 sec.
1/5 ms-1
Displacement of the sun with respect to earth is;
r
Instantaneous velocity is;
➡Positive
➡Negative
If the displacement=15 m and time=10 sec, the average velocity is;
1.5 m/s
A decrease in velocity per unit of time is called;
Acceleration
For a linear relationship between displacement and time, we get a d-t graph:
Straight Line passing through the origin
An object is moving with constant speed, which of the following is true?
Distance is greater than displacement
A stone is projected from the ground with a velocity of 25 m/s. 2 seconds later it just clears the wall 5m high. Then the angle of projection of the stone and the greatest height reached are:
➡60°
➡8.7m
Acceleration of moving car when brakes are applied;
Negative
The slope of the distance-time graph will always be;
Positive
The slope of the velocity-time graph represents
Acceleration
An object is accelerating:
When its speed or direction is changing
What is the slope of a straight line graph of position vs time?
Displacement
If the velocity versus time graph of an object is a horizontal line, the object is:
Moving with zero acceleration
The acceleration of a moving object can be found from;
The slope of the velocity-time graph
The coefficient of restitution for a perfectly elastic collision is;
1
Walking is possible on the account of;
Newton’s Third Law of Motion
The coefficient of restitution for a perfectly inelastic collision is;
Infinity
When two bodies stick together after the collision, the collision is said to:
Perfectly Inelastic collision
What is the accelerating force on the Diwali rocket if it ejects 0.05 kg of gases per second at a velocity of 400 m/s?
20N
If the mass is 2kg and the velocity is 35 m/s, then the momentum is:
70 kg m/s
If force is doubled by keeping mass constant then the acceleration would be;
Halved
Newton’s third law is derived from;
Newton’s 2nd Law
Force exerted by the wall on the water will be;
F=mv/t
If a car and Truck move with the same velocity and we applied the same force on both which body comes to rest first
Car
If the maximum horizontal range is 40m, then what will be the height attained by the projectile;
800m
(RtanΘ=4H)
According to the 2nd Law of motion, which is correct?
Acceleration is not related to mass
Car weight of 000 has a velocity of 50 km per hour. If a mass of 250 is placed in this then velocity becomes;
100
The dimension of momentum is the same as;
Impulse
Displacement time graph slope gives us a unit of:
m/sec
Kgm/s2 is equal to;
Force
In elastic collision which of the following is constant
Momentum
Kinetic friction is always than static friction:
Less
Momentum is the product of:
➡Mass
➡Velocity
The momentum of particle changes when;
➡Energy is changed
➡Force is applied
The speed of an object in a particular direction is called:
Velocity
The acceleration time graph for projectile motion will be;
Straight Line
A mass accelerates uniformly when the resultant force acting on it is:
Constant but not zero
Which law of motion defines force?
1st Law
If the velocity-time graph is parallel to the y-axis then acceleration
0
The body moves from rest with a constant acceleration of 5. It instantaneous speed at the end of 10 seconds is:
50
A train of length 200m is crossing a bridge 400m in length at speed of 36km/h. What is the total time by train to cross the bridge
60sec
A hunter aiming a bird in a tree should aim;
a little above the
The horizontal component of a bouncing ball is;
unaffected by gravity
A ball is dropped from a height of 10m. The ball is embedded in sand 1m and stops, then,
Only momentum remains conserved
Which of the following is momentum closely related to;
Impulse
An object will possess uniform motion as long as the;
the resultant force acting on it is zero
In an elastic collision of two particles, the following is conserved
The total kinetic energy of both the particles
The displacement is a;
Vector quantity
Projectile motion has ___ acceleration at each point of the trajectory
Constant
A projectile is launched with vertical kinetic energy K at angle Θ, then its variation with vertical displacement Y
Linear
Projectile when launched at 90 degrees with respect to horizontal then its trajectory is;
Linear
In which situation, distance is three times its displacement?
The object moves 20m towards east and 10m towards south
SI unit of acceleration is:
m/s2
If we are standing in a bus and when conductors apply a brake then we feel;
the pseudo force pushes backwards
Horizontal velocity vs time graph for a projectile motion is;
is constant
Acceleration of the object which starts rest to reach 20 m/s in 10 sec is;
2 m/s2
If a projectile is launched with 3m/s velocity at a 60-degree angle then at the highest point its horizontal velocity is;
1.5 m/s
If velocity varies with time in a quadratic manner, then acceleration:
Linearly varying
Vector is a quantity which:
follows the rule of vector addition
The amgnitude of the dispalement is:
straight line distance between the initial position and the final position of the body
The net force acting in an inertial frame is;
zero
An object moves 20m in 5 sec. What is the gradient of the displacement-time graph?
4
The circular motion of a particle while attached to a string centripetal acceleration is provided by:
Tension in the string
Passengers sitting in a stationary car experience a jerk when the car suddenly starts. This is due to:
inertia of rest
For a linear relationship between displacement and time we get a d-t graph as;
a straight line passing through the origin
At every point of the trajectory of the projectile which of the following quantities is always zero
Horizontal acceleration
Which unit is used in the measurement of displacement?
m/s
Acceleration of a moving car when brakes are applied is:
Negative
A horizontal line in displacement-time graph represents___
Body at rest
A motion with uniform negative acceleration can be represented on the displacement-time graph by:
a curve line with decreasing gradient
When an object moves in a straight line then;
its displacement is equal to the distance
If one body is at rest then if we try to move it then it will resist by:
Inertia of rest
If the velocity varies linearly with time then acceleration is called:
Uniform
Mass m1 has a velocity of 0m/s and mass m2 has a velocity of 5 m/s. Mass m1>m2.
Which one has larger inertia?
m1
Consider a car is travelling for one hour. In which of the following causes the average velocity is zero?
A car travels 30km due west, then turns around and travels 30km due east
Newton’s second law states that the rate of change of ___ is equal to external force:
Momentum
The velocity of an object changes from 20m/sec to 50 m/sec in 5 sec. What is the acceleration of the object?
6 m/s2
For a car which applies brakes from 10m/sec to stop the car in 10 sec its acceleration is:
-1 m/s2
Instantaneous velocity is defined as;
dx/dt