Physics 151 - Homework #4 - 15 points possible Instructions: Write your full solutions on separate paper, then scan and upload them in the submission area on Blackboard by the due date listed there. You must show all work to receive credit unless otherwise indicated. Be sure to label all problem numbers and circle your answers. 1. (1 pt) How are inertia and mass related? 2. (1 pt) A person pushes a 4.50 kg laundry cart in such a way that the net external force on it is 60.0 N. Calculate the magnitude of its acceleration. 3. (2 pts) At an instant when a soccer ball is in contact with the foot of a player kicking it, the horizontal, or x component of the ball's acceleration is 810 m/s and the vertical or y component of its acceleration is 1 100 m/s2. The ball's mass is 0.43 kg. What is (a) the magnitude and (b) the direction of the net force acting on the soccer ball at this instant? Express the direction by an angle measured relative to the x- axis. 4. (1 pt) A 35.0 kg dolphin decelerates from 12.0 to 7.50 m/s in 2.30 s to join another dolphin in play. What average force was exerted to slow him if he was moving horizontally? (You may assume the gravitational force is balanced by the buoyant force of the water, both of which may be neglected.) 5. (2 pts) An elevator filled with passengers has a total mass of 1800 kg. (a) The elevator accelerates upward from rest at a rate of 1.20 m/s for 1.60 s. Calculate the tension in the cable supporting the elevator during this time. (b) The elevator then continues upward at a constant velocity for 8.50 s. What is the tension in the cable during this time? (c) The elevator decelerates at a rate of 0.600 m/s for 3.00 s. What is the tension in the cable during the deceleration? (d) How high above its original starting point has the elevator moved? Hint: use the kinematics equations for part (d). 6. (2 pts) In the figure, a light-weight, taut, unstretchable cord B joins block 1 and the large-mass block 2. Cord A exerts a force on block 1 to the make it accelerate forward. (a) How does the magnitude of the force exerted by cord A on block 1 compare with the magnitude of the force exerted by cord B on block 2? Explain. (b) How does the acceleration of block 1 compare with the acceleration of block 2? Explain. B 2 7. (2 pts.) A 175 N bird feeder hangs from two support cables as shown in the figure. Find the tension in (a) the left cable and (b) the right cable. Bird 8. (2 pts.) Two blocks, each of mass 3.40 kg are fastened to the top of an elevator as shown in the figure. If elevator has an upward acceleration of 1.65 m/s', find the tensions (a) Ti and (b) T2. 1 ma 9. (2 pts.) Two objects with masses 3.00 kg and 5.00 kg are connected by an ideal string that passes over a frictionless pulley. Determine the (a) tension in the string and (b) acceleration magnitude of each object. 3.00 kg 5.00 kg
