H 5.5 4/4 points (graded) 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 (in kg) of the backpack? Give your answer to two significant figures without units. 10 V b. What does the scale read (in N) if the elevator moves upward while speeding up at a rate 3.8 m/s2? Give your answer to two significant figures without units. 136 V c. What does the scale read (in N) if the elevator moves upward at constant velocity? Give your answer to two significant figures without units. 98 V 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? Give your answer to two significant figures without units. 0 V H 5.6 2/2 points (graded) A roller coaster car starts from rest at the top of a track 30.0 m long and inclined at 20.0° to the horizontal. Assume that friction can be ignored. a. What is the acceleration ( in m/s2) of the car? Enter your answer to two significant fugures without unit. 3.35 V 3.35 b. How much time elapses (in sec) before it reaches the bottom of the track? Enter your answer to two significant fugures without unit. 4.2 V 4.2
H 5.7 3/3 points (graded) Two blocks are connected by a massless rope as shown below. 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. mi my a. Find the acceleration of the system in m/s2. Enter your answer to two significant figures without unit. 2 V 2 b. Find the tension (in N) in the rope. Enter your answer to two significant figures without unit. 7.8 V 7.8 c. Find the speed (in m/s) with which the hanging mass hits the floor if it starts from rest and is initially located 1.0 m from the floor. Enter your answer to two significant figures without unit. 2 V 2
H.W. 5.8 3/3 points (graded) Consider the 52.0-kg mountain climber shown below. 31º ? Flegs 15° a. Find the magnitute of the tension in the rope ( in N ) and the force that the mountain climber must exert with her feet on the vertical rock ( in N ) face to remain stationary. Assume that the force is exerted parallel to her legs. Also, assume negligible force exerted by her arms. Enter your answer to two significant figures without unit. Tension: 512 V 512 Force on the rock: > 273 273 b. What is the minimum coefficient of friction between her shoes and the cliff? Enter your answer to three significant figures without unit. 0.268 V 0.268