Dear all, here's some questions I need help in, kindly help me.
:D I don't need full answers, just guidance, thanks. I know there's
a lot of questions, but they are actually MCQ questions and won't
take too much of your time. (:
1) A crane has maximum safe working
load of 1.2 x 104 N and is used to lift a concrete
block of mass 1000 kg. What
is the maximum safe upward acceleration of the block while being
lifted?
2) The acceleration
of free fall is determined by timing the fall of a steel ball
photo-electrically as shown below. The ball passes P and Q at
time t1 and t2 after
release.
What is the acceleration of free
fall?
Tried using COE, but I still
have no idea how to do.
3) The minute hand of a large clock is 3.0 m
long. What is its mean angular speed?
Why isn't it found using
2pi/T?
4) A car of
mass m has an engine which can deliver
power P. What is the minimum time in which the car
can be accelerated from rest to a
speed v?
v = u + at
Given u = 0,
v = at
t = v/a
For minimum t, a = maximum.
I have no idea what follows.
5) A solid steel sphere is held just
below the surface of water and released. Its terminal
velocity v is measured. If the experiment were
repeated in places with different values
of g (the acceleration of free fall), a graph
of v against g would
most closely resemble
I need the proper
explanation for this.
6) The door
of a working refrigerator is left open. After some hours, the
temperature of the room in which the refrigerator is placed
is
a unchanged, because the refrigerator absorbs as
much heat as it gives out
b lower, because the refrigerator will extract
heat from the room
c unchanged, because the refrigerator is
thermostatically controlled
d higher, because the refrigerator gives out more
heat than it absorbs
e lower, because the coolant in the refrigerator
will evaporate much more rapidly
7) A light
spring has a mass of 0.20 kg suspended from its lower end. A second
mass of 0.10 kg is suspended from the first by a thread.
The arrangement is allowed to come into static equilibrium and then
the thread is burned through. At this instant, what is the upward
acceleration of the 0.20 kg mass?
(take g as 10 m
s-2)
I tried and got 10 which I
know is incorrect.
8) A body of mass 2 kg is moving on a
horizontal surface with a speed of 1.41 m
s-1 in
a north-easterly direction. A force of 0.2 N acting in a westerly
direction is applied to the body for 10 s. If friction is
negligible, the body is then moving with a speed
of
a) 0.41 m s-1 in a north-easterly direction
b) 1.00 m s-1 in a northerly direction
c) 1.41 m s-1 in a north-westerly direction
d) 2.24 m s-1 in a direction 63.4 ° east of north
e) 2.41 m s-1 in a north-easterly direction
I know that the direction
will be northerly, but how do you get 1.00?
9) The
force F required to extend a sample of rubber by a
length x was found to vary as shown in the
diagram.
What is the energy stored in the rubber for an
extension of 5m?
I calculated it to be 100,
but it's wrong. =/
10) An object of
mass m passes
a point X with a
velocity v and
slides up a frictionless incline to stop at point Y which is at a
height h above
X.
A second
object of mass
½ m passes
X with a velocity of
½ v.
To what height will it
rise?
I worked it out and
i got 1/8h, but the answer is 1/4h. Am I right or is the
answer wrong?
1/2 mv^2 = mgh ------
(1)
1/2 (1/2m) (1/2v)^2 = mg(xh) ------
(2)
Comparing (1) &
(2),
1/2 (1/2m) (1/4v^2) =
mg(1/8h)
11) The
formula for the period of a simple pendulum
is T = 2p (l/g).
Such a pendulum is used to
determine g.
The fractional error in the measurement of the
period T
is ±x and
that in the measurement of the
length l is
±y. The fractional
error in the calculated value
of g is no
greater than?
a) x + y
b) x - y
c) 2x - y
d) 2x + y
e) xy