Page 77 - Schaum's Outline of Theory and Problems of Applied Physics

62 LAWS OF MOTION [CHAP. 5

The acceleration of the box along the ramp is therefore
F mg sin θ 2 2
◦
a x = = = g sin θ = (9.8 m/s )(sin 40 ) = 6.3 m/s
m m
SOLVED PROBLEM 5.26
A force parallel to the ramp of what magnitude is needed to pull a 50-kg box up a frictionless ramp at an
2
◦
angle of 25 with the horizontal so that the box has an acceleration of 3 m/s ?
To give the box an upward acceleration of a x along the ramp, the applied force F must exceed the component
w x parallel to the plane of the box’s weight w by the amount ma x . From Fig. 5-9, w x = w sin θ = mg sin θ, so

2
2
F = mg sin θ + ma x = m(g sin θ + a x ) = (50 kg)[(9.8 m/s )(sin 25 ) + 3 m/s ] = 357 N
◦
Multiple-Choice Questions

2
5.1. Compared with her mass and weight on Earth, an astronaut on Venus, where the acceleration of gravity is 8.8 m/s ,
has
(a) less mass and less weight
(b) less mass and the same weight
(c) less mass and more weight
(d) the same mass and less weight

5.2. A car towing a trailer is accelerating on a level road. The car exerts a force on the trailer whose magnitude is
(a) the same as that of the force the trailer exerts on the car
(b) the same as that of the force the trailer exerts on the road
(c) the same as that of the force the road exerts on the trailer
(d) greater than that of the force the trailer exerts on the car

5.3. In Newton’s third law of motion the action and reaction forces
(a) act on the same object
(b) act on the different objects
(c) do not necessarily have the same magnitude and do not necessarily have the same line of action
(d) have the same magnitude but do not necessarily have the same line of action

5.4. A jumper of weight w presses down on the floor with a force of magnitude F, and the jumper leaves the floor as a
result. The force the floor exerted on the jumper must have had a magnitude
(a) equal to w and less than F
(b) equal to w and equal to F
(c) more than w and equal to F
(d) more than w and more than F

5.5. A force of 1.0 N acts on a 1.0-kg object that can move freely. The object’s acceleration is
(a) 0.102 m/s 2 (c) 1.0 m/s 2
(b) 0.5 m/s 2 (d) 9.8 m/s 2

5.6. A force of 1.0 N acts on a 1.0-N object that can move freely. The object’s acceleration is
(a) 0.102 m/s 2 (c) 1.0 m/s 2
(b) 0.5 m/s 2 (d) 9.8 m/s 2