Q
1: A football player kicks a football straight up in to the air with an initial
velocity of 25m/s. What is the approximate maximum height that the ball
reaches? Use acceleration due to gravity (g) as 9.8m/s2. Marks = 7
Ans:-
2as
= Vf2 – Vi2
Where
a = g = 9.8m/s2
Vf2
= 0
Applying
the values:
2as
= Vf2 – Vi2
2(9.8m/s2)
s = 0 – (25m/s)2
(19.6m/s2)
s = 625m2/s2
s
=625m2/s2 / (19.6m/s2)
s
= 31.8m
Q
2: In the classic horse and cart problem, a horse is attached to a cart that
can roll along on a set of wheels. Which of the following statement is true?
Also explain the reason of your selected choice as well.
a) The horse pulls on the cart with a force, and the cart
pulls, back on the horse with an equal force.
b)
The horse pulls on the cart with a force greater than the force that the cart
pulls back on the horse.
c)
The horse pulls the cart forward because the force of friction forward is
greater than the force of the wagon backward.
d)
The horse pulls the cart forward, because of a time delay between the action
and reaction forces.
e)
The horse pulls the cart forward, but only if the horse has a mass greater than
the mass of the cart. Marks = 6 (2+4)
Ans:-
c)
The horse pulls the cart forward because the force of friction forward is
greater than the force of the wagon backward.
Reason:-
The
forces on the cart include the forward force the horse exerts on the cart and
the backward force due to friction at the ground, acting on the wheels. At
rest, or at constant velocity, these two are equal in size, because the
acceleration of the cart is zero. The forces on the horse include the backward
force the cart exerts on the horse and the forward force of the ground on its
hooves. At rest, or at constant velocity, these two are equal in size, because
the acceleration of the horse is zero. The force the horse exerts on the cart
is of equal size and opposite direction to the force the cart exerts on the
horse, by Newton's third law. The horse places its feet so as to change the
angle of the force its hooves exert on the ground, thereby increasing the
backward force of its hooves on the ground.
Q
3: Is it true to say that a projectile has zero acceleration at its peak? If
yes explain if not give a reason. Marks = 4
Ans:-
The
acceleration due to gravity is constant at 9.8 m/sec^2. One of the
variables in projectiles is its speed --- it slows down as it goes up and gains
speed as it goes down. When the projectile reaches its maximum height, its
velocity is always zero. Acceleration has nothing to do with instantaneous
velocity. Acceleration shows the relationship between the velocities of the
projectile at 2 different points in time. If acceleration was zero, the
difference in velocity of the projectiles between any two points of its
trajectory would be 0. However, with an acceleration, even if the velocity of
the projectile at one point was 0, but the acceleration would not be zero
because the acceleration of a projectile is always equal to the acceleration of
gravity.
Q
4: (a) Anna is pushing but the box does not move. What is the force of static
friction shown in below figure? Marks = 3
Ans:-
Fs=mu*N
=1*7N
=7N
(b)
What is the maximum static friction force shown in below figure? The
coefficient of static friction for these materials is 0.31. Marks = 5
Ans:-
=0.31*27N
27
nai only 7 hai
or
answer hai 2.17
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