Unit Revision PQ9

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Calculate the work done by the forces in the following diagram

Only Fapp does work. Fgrav and Fnorm do not do work since a vertical force cannot cause a horizontal displacement.

Wapp= (10 N) * (5 m) *cos (0 degrees) = +50 Joules

Q7 Jarrad carries a 200-N suitcase up three flights of stairs (a height of 10.0 m) and then pushes it with a horizontal force of 50.0 N at a constant speed of 0.5 m/s for a horizontal distance of 35.0 meters. How much work does Jarrad do on his suitcase during this entire motion?

The motion has two parts: pulling vertically to displace the suitcase vertically (angle = 0 degrees) and pushing horizontally to displace the suitcase horizontally (angle = 0 degrees).

Q8 A force of 50 N acts on the block at the angle shown in the diagram. The block moves a horizontal distance of 3.0 m. How much work is done by the applied force?

Q9

A student with a mass of 80.0 kg runs up three flights of stairs in 12.0 sec. The student has gone a vertical distance of 8.0 m. Determine the amount of work done by the student to elevate his body to this height. Assume that his speed is constant.

The student weighs 784 N (Fgrav= 80 kg * 9.8 m/s/s). To lift a 784-Newton person at constant speed, 784 N of force must be applied to it (Newton's laws). The force is up, the displacement is up, and so the angle theta in the work equation is 0 degrees. Thus,

Q10

Calculate the work done by a 2.0-N force (directed at a 30° angle to the vertical) to move a 500 gram box a horizontal distance of 400 cm across a rough floor at a constant speed of 0.5 m/s.

In this problem, the d is horizontal and the F is at a 60-degree angle to the horizontal. Thus, theta is 60 degrees.

Unit Revision PQ10

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Q5 A horizontal force of 140 N is needed to pull a 60 kg box across the horizontal floor at constant speed. What is the value of the force opposing motion?

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Q10 Three blocks masses 2kg, 3kg and 5kg are connected to each other with light strings and are then placed on a smooth frictionless surface. See fig. below. Let the system be pulled with a force F from the side of lighter mass so that it moves with an acceleration of 1ms-2. T1 and T2 denote the tensions in the strings. Calculate the value of T1 and T2.

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Unit Revision PQ12

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Unit Revision PQ13

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