A hoist is used to lift a 780 kg car upward with an acceleration of 0.110 m/s². a) What is the net force acting on the car? b) What force was used to lift the car?

Chris, a recent physics major, wanted to design and carry out an experiment to show that an objects mass determines its inertia. He used an ultrasound device to measure acceleration of a low-friction cart attached to a hanging block to provide the same force on the cart during each run (Fig. P6.76A). Chris varied the mass of the cart by varying the number of lead rods placed in it. Chris used Newtons second law Fx=FT=Max to predict his results. He reasoned that because FT is the same for each run, the carts acceleration should be inversely proportional to its mass: ax=FTM=constantM(1) Chriss goal was to show that his data fit Equation (1). He decided to analyze his results by plotting ax as a function of 1/M; Equation (1) predicted that he should get a straight line, passing through the origin with a slope equal to the tension (red line in Fig. P6.76B): Chris ran several trials for each run, averaged his results and estimated the error. He then plotted his data (green line in Fig. P6.76B). Chris was excited to see that he correctly predicted that the data fell along a straight line: ax=(0.27N)1M(0.048m/s2) According to the straight-line fit to the data, the slope of the line is 0.27 N, which was close to the weight of the hanging mass and therefore close to the tension in the string. Chris, though, was disappointed to see that the line had a negative intercept. Mathematically, as M, 1M0. Chris was confused because he believed that as the mass increased, the carts acceleration should approach zero. He was quite sure that he did not discover some new property of inertia or mass. After convincing himself that he was not being careless in the laboratory and that his data were correct, he started to search for an explanation for the discrepancy between his prediction and his data. Help Chris find an explanation. FIGURE P6.76 A. Chriss experimental apparatus. B. Chriss prediction (red line) and experimental results (green line).

In a laboratory model of cars skidding to a stop, data are measured for four trials using two blocks. The blocks have identical masses but different coefficients of kinetic friction with a table: k = 0.2 and 0.8. Each block is launched with speed vi = 1 m/s and slides across the level table as the block comes to rest. This process represents the first two trials. For the next two trials, the procedure is repeated but the blocks are launched with speed vi = 2 m/s. Rank the four trials (a) through (d) according to the stopping distance from largest to smallest. If the stopping distance is the same in two cases, give them equal rank. (a) vi = 1 m/s, = 0.2 (b) vi = 1 m/s, k = 0.8 (c) vi = 2 m/s, = 0.2 (d) vi =2 m/s, k = 0.8

In Figure P1.84, the pulleys and the cord are light, all surfaces are frictionless, and the cord does not stretch. (a) How does the acceleration of block 1 compare with the acceleration of block 2? Explain your reasoning. (b) The mass of block 2 is m2 = 1.30 kg. Derive an expression for the acceleration of the block having mass m2 as a function of the mass of block 1, m1. (c) What does the result of part (b) predict if m1 is very much less than 1.30 kg? (d) What does the result of part (b) predict if m1 approaches infinity? (e) In this last case, what is the tension in the cord? (f) Could you anticipate the answers to parts (c), (d), and (e) without first doing part (b)? Explain. Figure P1.84