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PHYSICS 241 Assignment 6
Reading: Get a “freshman physics” book and read what you need to solve the problems. It's usually in the
chapter called “Applying Newton's Laws”.
Problems 13 Due in class Thursday 10/23/
Remaining Problems due next Thursday 10/30/
IN CLASS – 10/21/
IC1 An elevator moves upward at 5.2 m/s. What is the minimum stopping time it can have if the
passengers are to remain on the floor?
IC2 A towplane tows two identical gliders of mass m=500 kg each. Initially the three craft are traveling
at constant speed. The line joining the towplane to the first glider has a tension T=5000 N, which
overcomes the air resistance experienced by the two gliders together. (Assume both gliders experience the
same amount of drag). The two plane then begins to accelerate with acceleration 2 m/s*s. What is the new
tension in the first line? What is the new tension in the second line?
IC3 Blocks A and B, of equal mass, but connected by a massless wire, sit on a 40 degree ramp. Block B
has a friction coefficient of 0.2 with the ramp, but block A, on rollers, is frictionless.
a) What is the acceleration of the two block system down the ramp?
b) What is the tension in the wire joining them?
HOMEWORK
RS61 In a tractor pulling contest, a 2300kg tractor pulls a 4900kg sledge with an acceleration of 0.
m/s^2. If the tractor exerts a horizontal force of 7700 N on the ground, determine the magnitude of
(a) The force of the tractor on the sledge;
(b) The force of the sledge on the tractor;
(c) The frictional force exerted on the sledge by the ground, and the coefficient of friction between the sledge
and the ground.
RS62 You are designing an elevator for a hospital. The force exerted on a passenger by the floor of the
elevator is not to exceed 1.60 times the passenger's weight. The elevator accelerates upward with constant
acceleration for a distance of 3.0 m and then starts to slow down.
What is the maximum speed of the elevator?
RS63 A block is shoved up a 22degree slope with an initial speed of 1.4 m/s. The coefficient of kinetic
friction is 0.50, and the coefficient of static friction is 0.70.
(a) How far up the slope will the block get?
(b) Once stopped, will it slide back down?
RS64 A block sits on a ramp on the moon. The ramp makes angle
theta with the horizontal. The blockramp couple has a static friction coefficient
s
and a kinetic coefficient of
k
=0.2 . g
moon
=1.6 m/ s
2
.
a) The block starts at rest. For what value of theta will the block begin to move?
b) Once it begins to move, what acceleration will it experience?
RS65 A teflon (frictionless) ramp makes a 30 degree angle with horizontal. Blocks and A and B sit on the
ramp, attached to each other by a massless string. Block B has a hook on the uphill side. The hook is
attached to another string which goes over a frictionless/massless pulley to a third mass, C, which hangs
vertically from it.
a) Block C is chosen to just balance Blocks A and B so that all three masses are motionless. If Block A and
Block B have mass 4 kg and 12 kg respectively, what is the mass of block C?
b) What is the tension T in the line joining blocks A and B?
c) Block C is replaced by a more massive block D such that blocks A and B begin to accelerate up the ramp
and T increases by 50%. What is the mass of block D?
d) The teflon ramp is replaced by smooth wood so that there is now a friction coefficient of 0.1 between
blocks A and B and the ramp. What is the acceleration of the A,B, D system? What is the tension in each
of the two ropes?
RS66) A 4kg block of ice (frictionless) is subjected to a force in the positive xdirection.
a) If the block started from rest and moved d=20 m in 4 seconds, what is the magnitude of the
force?
b) After 4 seconds, the original force is replaced by a new force two thirds as great in magnitude
and pointed in the negative xdirection. What is the speed of the block 12 seconds later, and what
direction is it going (left or right?).
c) What is the displacement from the origin of the block at this time? (and is it to the left or right
of the origin?)
d) What is the average velocity of the block of ice over the entire 16 second interval?
RS67) An object of mass m=8 kg begins at the origin with some speed v0. You apply a force
F
1
i−2.
j (^) N to the object, and some time later, it arrives at the position r 1
i 42
j
m.
a) How much work have you done on the object?
b) What is its speed when it arrives at r 1
RS68) A hockeypuck sits on a platform rotating at 10 rpm. Given a coefficient of static friction
s
=0.2 (^) , how far can the puck be from the center before it slides off?
RS69) You apply a constant force F pushing 4 blocks to the left as shown by the black arrow.
There is a spring between blocks A and B with constant k. As a result of your force the spring is
