# Homework Help: Energy Questions

1. Mar 7, 2006

### kfink85

Here are a couple problems that I have been attempting to do but I am not sure if I am doing them right.

1. A block of mass 2.50 kg is pushed 2.20 m along a frictionless horizontal table by a constant 16.0-N force directed 25 degrees below the horizontal. Determine the work done by (a) the applied force, (b) the normal force exerted by the table, (c) the force of gavity, and (d) the net force on the block.

(a) W = Fcos(pheta)*Delta X
W = ( 16 cos 25 )( 2.2 )
W= 31.95 J

(b) 0 since it is perpendicular to the displacement
(c) 0 since it is perpendicular to the displacement

2. An outfielder throws a 0.150-kg baseball at a speed of 40.0 m/s and an initial angle of 30 degrees. What is the kinetic energy of the ball at the highest point of its motion?

I know that Vy= 0 m/s at the top of the motion but I'm not sure if this information is even relevant. Do I need to break this down in to vectors or no?

I know KE=1/2mv^2. Do I just plug it in or is the velocity going to be changed at the top due to vectors?

Thank you in advance to anyone that can help.

2. Mar 7, 2006

### kfink85

Anyone have any idea?

3. Mar 7, 2006

### lightgrav

The Work done by the "net Force" is what changes the KE.

The horizontal component of velocity (at throw) is the only component at peak.

4. Nov 16, 2010

### favvkes1993

1 d) same as part a) because table is horizontal and firctinless, so only work acting on block is force of the push