## The acceleration of One of Four rockets Burning| Newton’s Second Law of Motion: Concept of a System| Dynamics| College Physics| Problem 4.7

### (b) Why is the acceleration not one-fourth of what it is with all rockets burning? ## Force Exerted by a Lawnmower| Newton’s Second Law of Motion: Concept of a System| Dynamics| College Physics| Problem 4.5

### In Figure 4.7, the net external force on the 24-kg mower is stated to be 51 N. If the force of friction opposing the motion is 24 N, what force F (in newtons) is the person exerting on the mower? Suppose the mower is moving at 1.5 m/s when the force F is removed. How far will the mower go before stopping? Figure 4.7 The net force on a lawn mower is 51 N to the right

## Measuring the mass of an Austronaut| Newton’s Second Law of Motion: Concept of a System| Dynamics| College Physics| Problem 4.4

### Since astronauts in orbit are apparently weightless, a clever method of measuring their masses is needed to monitor their mass gains or losses to adjust diets. One way to do this is to exert a known force on an astronaut and measure the acceleration produced. Suppose a net external force of 50.0 N is exerted and the astronaut’s acceleration is measured to be 0.893 m/s² (a) Calculate her mass. (b) By exerting a force on the astronaut, the vehicle in which they orbit experiences an equal and opposite force. Discuss how this would affect the measurement of the astronaut’s acceleration. Propose a method in which the recoil of the vehicle is avoided.

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