Question

1. Renee is on Spring Break and pulling her 21-kg suitcase through the airport at a constant speed of 0.47 m/s. She pulls on the strap with 120 N of force at an angle of 38° above the horizontal. Assume the ground to be flat,

   • Draw a FBD showing the forces on the suitcase.

   • Find the acceleration of the suitcase.

   • Determine the normal force experienced by the suitcase.

   • Determine the total resistive force (friction) experienced by the suitcase.

   • Find the coefficient of kinetic friction.

   • Which coefficient of friction is higher: static or kinetic. Explain why.

2. It’s easy to build your own accelerometer! It consists of a ball on a string hanging fromthe roof of your car. When the car is stopped or cruising at a constant speed, the ball hangs straight down. But, when it is accelerating as in the picture, the ball hangs down atan angle, which we’ll call θ.

   • Draw the free body diagram on the ball.

   • What is the acceleration in the y-direction?

   • Write Newton’s law in the y-direction and leave it in terms of symbols.

   • Write Newton’s law in the x-direction and leave it in terms of symbols.

   • You now want to try out your new accelerometer, so you get in your car and hit

     the gas. As you accelerate, you notice the ball hanging down with an angle of θ = 7.0o. How fast were you accelerating?

3. A truck of mass m is connected to a trailer by a rope. The rope can carry 7,000 N before it breaks. The truck now starts pulling the trailer with an external force.

   • Draw a free-body diagram of this situation. (Be sure to include friction.)

   • The trailer accelerates at 3 m/s2. As it drags across the ground, a frictional force

     of 1,000 N acts in the direction opposite its motion. However, the rope breaks.Using the rope’s breaking strength of 7,000 N, what can you say about the mass of the trailer?

   • What is the normal force acting on the trailer?

   • What is the coefficient of kinetic friction present?

4. On her way to visit her grandmother Grangran, Red Riding Hood sits down to rest and places her 1.2kg basket of chocolate, cupcakes, and cookies beside her. A wolf comes along, spots the basket of goodies, and cannot resist the sweet smell. He begins to pull on the handle with a force of 6.4N at an angle of 250 on the right of the vertical. Red is not going to let her sweets go without a fight, so she pulls on the handle with a force of 12N. As a passerby, you see that the net force on the basket is straight up.

• Instead of helping Red, you decide to sit down and figure out at what angle she is pulling. What angle do you get?

• The wolf is able to fight off Red Riding Hood and lifts the 1.2 kg basket of goodies to his nose to smell the sweet smell. He lifts the basket vertically with his paws at a constant upward velocity of 1.5 m/s. What is the magnitude of the totalforce of the wolf’s paws on the basket?

Answer 1