PHYS 2211 Module 6 Self Assessment Practice Problems

Module 6 Self Assessment Practice Problems


Find the tension in each of the three cables supporting the traffic light if it weighs 200 N.
Answer: T1 = 93.6 N, T2 = 156 N, T3 = 200 N
A 20.0-g ball hangs from the roof of a freight car by a string. When the freight car begins to move, the string makes an angle of 35.0° with the vertical.
(a) What is the acceleration of the freight car?
(b) What is the tension in the string?
Answer: (a) 6.90 m/s2 (b) 0.24 N
A student’s backpack, full of textbooks, is hung from a spring scale attached to the ceiling of an elevator. When the elevator is accelerating downward at 3.8 m/s2, the scale reads 60 N.
(a) What is the mass of the backpack?
(b) What does the scale read if the elevator moves upward while speeding up at a rate 3.8 m/s2 ?
(c) What does the scale read if the elevator moves upward at constant velocity?
(d) If the elevator had no brakes and the cable supporting it were to break loose so that the elevator could fall freely, what would the spring scale read?
Answer: (a) 10 kg (b) 140 N (c) 98 N (d) 0 N

Two blocks are connected by a massless rope as shown. The mass of the block on the table is 4.0 kg and the hanging mass is 1.0 kg. The table and the pulley are frictionless.
(a) Find the acceleration of the system.
(b) Find the tension in the rope.
(c) Find the speed with which the hanging mass hits the floor if it starts from rest and is initially located 1.0 m from the floor.
Answer: (a) 2.0 m/s2 (b) 7.8 N (c) 2.0 m/s
Suppose you have a 120-kg wooden crate resting on a wood floor, with coefficient of static friction 0.500 between these wood surfaces.
(a) What maximum force can you exert horizontally on the crate without moving it?
(b) If you continue to exert this force once the crate starts to slip, what will its acceleration then be? The coefficient of sliding friction is known to be 0.300 for this situation.
Answer: (a) 588 N (b) 1.96 m/s2
Calculate the deceleration of a snow boarder going up a 5.00° slope, assuming the coefficient of friction for waxed wood on wet snow µk = 0.1.
Answer: 1.83 m/s2
A machine at a post office sends packages out a chute and down a ramp to be loaded into delivery vehicles.
(a) Calculate the acceleration of a box heading down a 10.0° slope, assuming the coefficient of friction for a parcel on waxed wood is 0.100.
(b) Find the angle of the slope down which this box could move at a constant velocity. You can neglect air resistance in both parts.
Answer: (a) 0.737 m/s2 (b) 5.71°
A car rounds an unbanked curve of radius 65 m. If the coefficient of static friction between the road and car is 0.70, what is the maximum speed at which the car can traverse the curve without slipping?
Answer: 21 m/s
An airplane flies at 120.0 m/s and banks at a 30° angle. If its mass is 2.50 × 103 kg,
(a) what is the magnitude of the lift force?
(b) what is the radius of the turn?
Answer: (a) 28300 N (b) 2540 m

For a human body falling through air in a spread-eagle position, the magnitude of the drag force can be calculated with FD = Dv2, where the numerical value of D is about 0.25 kg/m.
(a) What value of D is required to make the terminal velocity vt = 42 m/s for a 50-kg skydiver?
(b) If the skydiver’s daughter, whose mass is 45 kg, is falling through the air and has the same D (0.25 kg/m) as her father, what is the daughter’s terminal speed?
Answer: (a) 0.28 kg/m (b) 42 m/s