# Physics 6A Practice Midterm #2 solutions 1. A locomotive engine of mass M i

The Above Picture is Related Image of Another Journal

## Physics 6A Practice Midterm #2 solutions 1. A locomotive engine of mass M i

Carlos Albizu University, US has reference to this Academic Journal, Physics 6A Practice Midterm #2 solutions 1. A locomotive engine of mass M is attached so that 5 train cars, each of mass M. The engine produces a constant force that moves the train forward at acceleration a. If 3 of the cars are removed, what will be the acceleration of the shorter train? We just use Newton?s 2nd law here: Net force = (total mass) x (acceleration) Initially, the total mass is 6M (5 cars, plus the engine) After removing 3 cars the total mass is 3M (2 cars, plus the engine) In both cases the Net force is the same (the engine didn?t change). Here is the formula in both cases: Initial F = (6M)(a) Final F = (3M)(afinal) Setting these equal gives afinal = 2a Another way so that think about this one is that since the mass is cut in half, the acceleration must double. We can think of this as a single box alongside total mass 4kg. Then using F = ma we get the acceleration of the whole system. Now we do the same thing, but just in consideration of box B: Remember ? Box B has a mass of only 3kg 2. Two boxes are placed next so that each other on a smooth flat surface. Box A has mass 1 kg in addition to Box B has mass 3 kg. A constant horizontal force of 8 N is applied so that Box A. Find the force exerted on Box B.

Related University That Contributed for this Journal are Acknowledged in the above Image

Now we need so that find the friction force. For this we need the Normal force on B. From the diagram we see that NB = mBg. Since the blocks are in motion, we are dealing alongside kinetic friction. Now we can substitute into the force formula: 5. Blocks A in addition to B in addition to C are connected by a massless string in addition to placed as shown, alongside Block A on the upward slope of the 60ø incline, Block B on the horizontal surface at the top in addition to Block C on the downward slope of the 60ø incline. The string passes over a frictionless, massless pulley. The inclines are frictionless, but the horizontal surface has coefficient of kinetic friction 0.45. Blocks A in addition to B have mass 5kg. The system accelerates at 2 m/s2. Find the mass of Block C. A bit of algebra will get us the desired mass mC 6. A 0.2 kg piece of wood is being held in place against a vertical wall by a horizontal force of 5 N. Find the magnitude of the friction force acting on the wood. 5N N mg Ffriction From the force diagram, we can see that the friction force must equal the weight of the piece of wood so that keep it from falling. 7. A 4 kg block on a horizontal surface is attached so that a spring alongside a force constant of 50 N/m. As the spring in addition to block are pulled forward at constant speed, the spring stretches by 25 cm. Find the coefficient of kinetic friction between the block in addition to the table. The key phrase here is ?constant speed?. Since the block is moving at constant speed (and direction) we know that its acceleration is 0. Thus the net force is 0 as well. Here is the force diagram. Since the net force is 0, we know that the Normal force must equal the weight, in addition to the Friction force must equal the Spring force. The spring force obeys Hooke?s Law: The weight is: Finally, we can put this together so that find the friction:

Physics 6B Standing Waves Standing Waves Standing Waves