Question

The pick-up truck in front of you is braking while it is moving towards a red light. The truck is moving to the right (as shown in the figure below). There is a heavy box in the back of the pick-up truck that is not secured by a rope or in contact with any side wall. You observe that the box is not sliding while the truck is braking. The friction force acting on the box is Ff=−114 N. The mass of the truck is mT=1500 kg and the mass of the box is m=45 kg. Note: The direction pointing to the right is considered to be positive. Answer the following two questions:

a) What is the acceleration of the truck? (Use a negative number for an acceleration that is directed to the left and no sign for an acceleration directed to the right.)

5b) Assume that the mass of the box on the truck in the previous question is doubled and the acceleration of the truck is doubled. Everything else remains unchanged. The magnitude of the friction force acting on the box is:

a) Twice as large as the previous value

b)Four times as large as the previous value

d)The same as before

e) Half the size as before

f) A quarter of the previous value

Answer 1