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"Basic Concepts of Physics" course objective is to introduce the terms like: Newton’s Motion Laws, Momentum, Energy, Rotation, Gravity, Liquids, Gases, Plasmas, Heat, Vibrations and Waves, Sound, Electrostatics, Electric current, Magnetism, Electromagnetic Induction, Properties of Light, Color.These questions are about: Newton’S 1St Law, Linear Motion, Momentum, Energy, Rotation, Gravity, Energy Conservation, Angular Momentum , Acceleration, Mechanical Energy
Typology: Exercises
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When in a subway car that suddenly stops, you lurch forward.
What’s the best explanation for this? A) Because of Newton’s 1
st^
law – you have inertia.
B) Because you have no accelerationC) Because of action-reaction forces between the car and youD) Because of the support force
When in a subway car that suddenly stops, you lurch forward. What’s the best explanation for
this? A)
Because of Newton’s 1
st^ law – you have inertia.
B)
Because you have no acceleration C)
Because of action-reaction forces between the car and you D)
Because of the support force Answer A: Newton’s 1
st^
law says that objects (you)
tend to keep moving in a straight line; inertiaresists changes in motion
According to Newton's law of inertia, a rail road train in motion should continuegoing forever even if its engine is turned off. We never observe this becauserailroad trainsA) move too slowly.B) must go up and down hills.C) are much too heavy.D) always have forces that oppose their motionAnswer: DHow about if there was
no
friction and no air drag – then
what would happen once the engine is turned off?Then the train would be accelerating while the engine wason, and would stop accelerating once the engine is turnedoff – i.e would move at constant velocity.
A hockey puck is set in motion across a frozen pond. If ice
friction and air resistance are neglected, the force requiredto keep the puck sliding at constant velocity is A) equal to the product of its mass times its weight.B) equal to its weight divided by its mass.C) zero.D) equal to its weight
As you’re sitting in your chair, your weight acts as adownward force on the chair. Why then does the chair notsink into the ground?A)
because of its weight
because it feels an upward directed support force
from the ground it is pushing down onC)
because of inertia – the resistance to changes in
motion.D)
because of momentum conservation.
As you’re sitting in your chair, your weight acts as a downward force on thechair. Why then does the chair not sink into the ground?A)
because of its weight
B)
because it feels an upward directed support force from the ground it
is pushing down onC)
because of inertia – the resistance to changes in motion.
D)
because of momentum conservation.
Answer: B, the chair is in equilibrium, there iszero net force on it. The gravitational force isequal and opposite to the upward support force.
A skier covers a distance of 3 m in half a second. What is his averagespeed? A) 1.5 m/sB) 3 m/sC) 6 m/sD) 9 m/s
C) Average speed =distance/time = 3m/0.5s = 6 m/s
As an object freely falls downward, itsA) velocity increasesB) acceleration increases.C) both of theseD) none of these.
When a rock thrown upwards falls back down and passes the
same point it was thrown from, a) its velocity is zero and its acceleration is zerob) its velocity is zero and its acceleration is about 10 meters per
second per second c) its velocity is about 10 m/s and its acceleration is zerod) its velocity is negative of the initial velocity it was thrown up with
and its acceleration is about 10 meters per second per second.
When a rock thrown upwards falls back down and passes the same point it was thrown
from, a)
its velocity is zero and its acceleration is zero b)
its velocity is zero and its acceleration is about 10 meters per second per second c)
its velocity is about 10 m/s and its acceleration is zero d)
its velocity is negative of the initial velocity it was thrown up with and its accelerationis about 10 meters per second per second.
Answer d) Note, acc. in free-fall (on earth) is
always
g~10 m/s
2
Half a second after starting from rest, a free-falling object will have a speed
of about a)
10 m/s b)
20 m/s c)
5 m/s d)
0 e)
None of these
Answer c) In free fall, object gains about 10m/s everysecond. So, in half a second, gain 5 m/s.
What if the free-falling object is moving upward at a speed of 20 m/s.What is its speed half a second later?
15 m/s since it loses 10m/s everysecond…
What is it’s acceleration at that time?
a = g = 10 m/s
2 downwards, always
for free-fall
Two balls are thrown from the same point high on a cliff. One
is thrown upwards and the other is merely dropped fromrest. Neglecting air resistance, which has the higheracceleration? A) The ball thrown upwardsB) The ball dropped from restC) It depends on how fast the thrown ball was thrownD) It’s the same for eachE) None of these
If a projectile is fired straight up at a speed of 10 m/s,the total time to return to its starting position is aboutA) 2 seconds.B) 10 seconds.C) 20 seconds.D) 1 second.E) not enough information to estimate
If a projectile is fired straight up at a speed of 10 m/s, the total time toreturn to its starting position is aboutA) 2 seconds.B) 10 seconds.C) 20 seconds.D) 1 second.E) not enough information to estimate
Answer: AEach second it loses about 10m/s so after 1s, ithas zero velocity, i.e. is turning around. Then itgains 10m/s as it falls, so after another second (atotal of 2 s) it has -10m/s i.e. same initial speed atwhich it began, hence returned to the same point.
So, if you’re told an object thrown directly upwards from the ground spends 2sin the air before returning to ground (= it’s “hang-time”), then you know thespeed it was initially kicked up with was 10 m/s.
