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ĐỀ THI HỌC SINH GIỎI CẤP TỈNH MÔN: VẬT LÝ ĐỀ Thời gian: 150 phút Sở GD & ĐT Cà Mau Đề thức Bài (4 điểm) Có hai người xe đạp khởi hành A B x x lúc hai địa điểm khác A B, cách AB = 5km đường thẳng chiều Sau người nhanh đuổi kịp người chậm Biết hai người chuyển động hai người với vận tốc 20km/h a) Tìm vận tốc người xe đạp lại b) Sau thời gian bao lâu, kể từ lúc bắt đầu chuyển động, khoảng cách hai người 10km ? Bài (3 điểm) Người ta pha trộn đồng bạc với để tạo thành hợp kim có khối lượng riêng D Cho biết khối lượng riêng đồng D1, bạc D2 Tính tỉ lệ K khối lượng đồng bạc cần phải pha trộn ? Bài (4 điểm) Cho mạch điện có sơ đồ hình vẽ: R R R V1 V2 V3 Các vôn kế giống có điện trở R v Vôn kế V1 U1 = 10V; vôn kế V3 U3 = 8V Tính số vôn kế V2 TaiLieu.VN Page Bài (3 điểm) Người ta bỏ vào nhiệt lượng kế chứa m = 300g nước 20oC khối hợp kim nhôm thiếc có khối lượng tổng cộng m = 2kg 150 oC Khi cân nhiệt, nhiệt độ hệ thống 30 oC Biết nhiệt dung riêng nước C = 4200 J/kg.độ, nhôm C2 = 900 J/kg.độ, thiếc C3 = 230 J/kg.độ bỏ qua hấp thu nhiệt nhiệt lượng kế nhiệt toả môi trường xung quanh Tính khối lượng nhôm thiếc có hợp kim Bài (3 điểm) Có điện trở loại R0 = 3Ω Hỏi cần mắc với để có điện trở tương đương đoạn mạch R = 5Ω ? Vẽ sơ đồ mạch điện Bài (3 điểm) Vật sáng AB cao 2cm đặt vuông góc với trục thấu kính hội tụ, điểm A trục Thấu kính hội tụ có tiêu cự 20cm vật AB đặt cách thấu kính 30cm a) Vận dụng kiến thức hình học, tính khoảng cách từ ảnh đến thấu kính Ảnh thật hay ảo ? Chiều cao ảnh A’B’ AB qua thấu kính ? b) Khi vật AB di chuyển lại gần thấu kính ảnh A’B’ có đặc điểm ? (thật hay ảo, chiều hay ngược chiều với AB, nhỏ hay lớn vật) - HẾT - TaiLieu.VN Page