题目内容

A high-diver of mass 70 kg jumps off a board 10 m above the water. If, 1.0 s after entering the water his downward motion is stopped, what average upward force did the water exert（）

A. 100 N
B. 686 N
C. 980 N
D. No answer is correct
E. 0 N
F. 10 N

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A girl and her bicycle have a total mass of 40 kg. At the top of the hill her speed is 5.0 m/s. The hill is 10 m high and 100 m long. If the force of friction as she rides down the hill is 20 N, what

A. 5.0 m/s
B. 10 m/s
C. 11 m/s
D. She stops before she reaches the bottom
E. 16 m/s
F. 19 m/s

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A block is projected with speed v across a horizontal surface and slides to a stop due to friction. The same block is then projected with the same speed v up an incline where is slides to a stop due t

A. This problem cannot be solved since it was not indicated whether the horizontal surface and the incline both had the same coefficient of kinetic friction
B. The case on the horizontal surface had the least decrease in total mechanical energy
C. The case on the inclined surface had the least decrease in total mechanical energy
D. In both cases the decrease in mechanical energy was the same
E. None of the others

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A truck loaded with sand accelerates along a highway. The driving force on the truck remains constant. What happens to the acceleration of the truck as its trailer leaks sand at a constant rate throug

A. It decreases at a steady rate
B. It increases at a steady rate
C. It increases and then decreases
D. It decreases and then increases
E. It remains constant
F. None of these

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A large crate of mass m is placed on the back of a truck but not tied down. As the truck accelerates forward with an acceleration a, the crate remains at rest relative to the truck. What force causes

A. the normal force
B. the force of gravity
C. the force of friction between the crate and the floor of the truck
D. the “ma” force
E. none of these

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A high-diver of mass 70 kg jumps off a board 10 m above the water. If, 1.0 s after entering the water his downward motion is stopped, what average upward force did the water exert（）

A. 100 N B. 686 N C. 980 N D. No answer is correct E. 0 N F. 10 N

A girl and her bicycle have a total mass of 40 kg. At the top of the hill her speed is 5.0 m/s. The hill is 10 m high and 100 m long. If the force of friction as she rides down the hill is 20 N, what

A block is projected with speed v across a horizontal surface and slides to a stop due to friction. The same block is then projected with the same speed v up an incline where is slides to a stop due t

A truck loaded with sand accelerates along a highway. The driving force on the truck remains constant. What happens to the acceleration of the truck as its trailer leaks sand at a constant rate throug

A large crate of mass m is placed on the back of a truck but not tied down. As the truck accelerates forward with an acceleration a, the crate remains at rest relative to the truck. What force causes

A. 100 N
B. 686 N
C. 980 N
D. No answer is correct
E. 0 N
F. 10 N