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a small block is pulled along a rough horizontal surface at a constant speed of 3m/s by a constant force. The magnitude of the force is 30N and acts at an angle of 30 degrees to the horizontal. Calculate the work done by this force in 10 seconds

Work done is: WD = Force x Distance moved in the direction of the force. It gives you a speed and a time, so you should be able to work out distance from that? Once you have distance, IF you have 30N applied in the SAME direction as the movement then it would simply be 30N x distance. However, the force in your question is a 30 degrees to the movement so you have to work out the component (the amount of) the force that goes in that direction. Hint: You need to use trigonometry to work out some much of the force is in that direction. Have a go and if you are still stuck post again and I will help further. 
Dr Anthony E.
17 April 2016
http://imgur.com/qBm04p3 I did a quick picture of how it works. The formula for work done is force * cos (angle) * displacement, f*cos(a)*s. The displacement, distance, is 10s*3m/s=30m.  The force is 30N. Cos a is about 0.866. Multiply them all together, 30N*0.866*30M=779J. Hope this helps.
18 April 2016
Always start by drawing a diagram! Then label the forces and directions. Then apply the equations:Work= Force in the direction of movement * DistanceCos(30)=adjacent/hypotenuse(30N)Distance= speed*timeRearrange this to find the adjacent, which is the component of  the force in the direction of motion, and multiply this by the distance!
22 April 2016
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